The issue of organizational sustainability has increasingly received a lot of research attention as it turned out that sustainable organizations positively contribute to multiple aspects of the society, including economic, environmental, and social (human) dimensions [
1,
2]. Particularly, over the last two decades, scholars in the field of human resource and organizational behaviors have paid great attention to employees’ sustainable engagement at their work as to the way of being beneficial in human performance. Since several scholars, such as Shuck and Wollard [
3], triggered fervent discussions of meanings and roles of work engagement of employees in the workplace (e.g., what work engagement means; why it matters; and what strategic interventions can be made in the Human Resource Development perspective), myriad theoretical and empirical studies on work engagement to explain and verify its importance in relation to various consequences in an organization have been conducted. Specifically, underpinning the conservation of resource (COR) theory and job demands and resources (JD-R) model as a theoretical frame of their work, many prior studies posited and tested work engagement as a mediator between antecedents (e.g., job resources [autonomy, skill variety, social support, performance feedback, supervisor coaching, opportunities for development, and learning culture], personal resources [self-efficacy, optimism, and organizational-based self-esteem], and job demands [overload, physical and emotional demands, and work–home interference]) and consequences (e.g., performance, turnover intention, organizational citizenship behaviors, innovative behaviors, customer satisfaction, and financial returns) [
4,
5,
6,
7,
8,
9,
10,
11]. Chughtai and Buckley [
12], for instance, found the crucial role of work engagement was that it plays as a mediator that links job resources (trust in supervisor and trust propensity) with employees’ in-role performance. Personal resources (self-efficacy, mental and emotional competences) were also found to have a positive impact on employees’ performance via work engagement [
13]. As such, work engagement acts as an important mediator that contributes to a link between various resources of employees and their outcomes. However, a question still remains: Is a mediating role of work engagement indispensable (significantly important), or minor and supplementary (so-called ‘nice-to-have’) that feebly benefits the impacts of individuals’ resources on consequences? The aim of the current study, therefore, is to test the role of work engagement as a mediator between job and personal resources as they relate to employees’ outcomes, namely job performance and turnover intention, specifically focusing on demonstrating whether work engagement is essential. To that end, the following research questions were established:
RQ1. Does work engagement play a crucial role as a mediator in the relationships of job and personal resources with job performance?
RQ2. Does work engagement play a crucial role as a mediator in the relationships of job and personal resources with turnover intention?
The present study contributes to the literature on work engagement in several important ways: First, given that work engagement is influenced by both external environments and internal (individual) factors [
14], simultaneously considering job resources and personal resources in relation to work engagement are necessary for better understanding of their linkage. However, based on our review of the literature, we recognized many scholars have considered either job or personal resources alone and/or more scholars were likely to focus on job resources as predictors. Thus, our study, that includes both diverse job and personal resources as antecedents of engagement, can expand the extant literature and provide meaningful insights for HR practitioners.
Secondly, plenty of scholars revealed the importance of work engagement as a mediator between resources and organizational outcomes. Nevertheless, because mediating roles of work engagement attain strong theoretical reasoning, based on the JD-R model of work engagement as a research framework, we have never attempted to focus on how significant work engagement is as a mediator. Thus, by comparing conceptualized models (i.e., one model for job and personal resources having direct effects on outcomes and indirect effects through work engagement versus the other model for job and personal resources having only indirect effects on outcomes through work engagement) and finding the best model, we could grasp how work engagement works on the underlying mechanisms by which the resources increase employees’ outcomes.
Lastly, our study originated in Korean organizations, while a majority of the studies on work engagement have been conducted in Western settings. Korean organizations, where job mobility has highly increased, seek to find strategic solutions and interventions to obtain engaged employees [
15]. According to the Global Workforce Study conducted by Towers Watson [
16], only 6% of Korean respondents (employees) were highly engaged in their work, while 48% of respondents were disengaged. This engagement level of Korean employees is much lower than the global average rate (engaged—21%; disengaged—38%). Given the clear connection between engagement and retention [
17], we believe our context-specific findings would help HR practitioners in Korean organizations develop effective and pragmatic interventions supported by empirical evidence.
1.1. Literature Review
This section reviews the concepts of job resources and personal resources, work engagement, job performance, and turnover intention. We reviewed definitions for each construct and relationships among those constructs. To answer our research questions, we gathered information on work engagement and examined whether work engagement can be considered a critical mediator that influences relationships between job and personal resources on employee outcomes, such as job performance and turnover intentions [
18,
19].
As various engagement frameworks exist, scholars have used a particular framework that explains the model of each study. The well-established JD-R model assumes that work characteristics may enhance work engagement, which in turn, improve organizational outcomes [
5]. We have attempted to expand the JD-R model because the past models have stressed the connection between employees’ job resources and well-being, including their work engagement [
20]. In addition, we used social exchange theory (SET) [
21] as a general framework to explain how employees’ perceptions of job and personal resources can affect employees’ performance-related outcomes and the impact of work engagement as an intervening mechanism. The reason for using SET is based on two assumptions: “(a) [P]eople should help those who have helped them, and (b) people should not injure those who have helped them” [
22]. For example, Richardsen, Burke and Martinussen [
23] also applied SET when explaining statistically significant relationships of work engagement between antecedents (e.g., personal characteristics, job demands, and job resources) and consequences (e.g., work outcomes).
1.2. Work Engagement
Researchers on engagement have developed various concepts to explain employee activities, behaviors, and psychological states (e.g., commitment, motivation, and satisfaction) as core components of engagement. Scholars have begun using engagement with different terminology (e.g., employee engagement, job engagement, and work engagement). Employee engagement refers to “the individual’s involvement and satisfaction with as well as enthusiasm for work” [
24]. Typically, employee engagement is comprised of both job and organizational engagement [
25]. Job engagement focuses on “a psychological state of fulfillment with one’s task at work” [
26] and organizational engagement focuses on “a multidimensional motivational concept reflecting the simultaneous investment of an individual’s physical, cognitive, and emotional energy in active, full work performance” [
27]. Work engagement (as used in this paper) is defined as “a positive, fulfilling, work-related state of mind that is characterized by vigor, dedication, and absorption” [
28]. Although these related terms have slightly different definitions, each definition shares a common core: To describe a state of mind [
29].
1.3. Job and Personal Resources
We have reviewed two concepts of job and personal resources as we used both variables in a single structural equation model. Job resources are “those psychological, social, or organizational aspects of the job that (a) are functional in achieving work-related goals, (b) reduce job demands and the associated physiological and psychological costs, and (c) stimulate personal growth and development” [
30]. Personal resources can be defined as an “individuals’ sense of their ability to control and impact upon their environment successfully” [
30].
For this study, we included job resources as antecedents of work engagement. Examples of job resources are autonomy, performance feedback, and skill variety. We examined personal resources as one of the critical pieces of work engagement. This study focused on three personal resources: Optimism, self-efficacy, and organizational-based self-esteem [
11,
14,
30,
31].
Previous researchers found job resources which improve work engagement and work-related outcomes [
13,
17,
32]. Salmela-Aro and Upadyaya [
17] used team climate, work ability, and role in the organization as job resources. According to their research, strongly favorable attitudes among employees toward job resources have led to better work engagement and reduced voluntary turnover. A longitudinal study by Hu et al. [
33] indicated that employees who experience high job resources showed a significant increase in work engagement and decrease in burnout.
Researchers noted that personal resources significantly influence job performance through work engagement [
34,
35,
36,
37]. Alessandri et al. [
34] studied whether the relationship between positive orientation and job performance is mediated by work engagement. Additionally, they examined the moderating effects of self-efficacy beliefs, an element of personal resources, among these relationships. Interestingly, work engagement partially mediated the relationship between positive orientation and job performance because the relationship was significant when employees’ self-efficacy was high or medium. Salmela-Aro and Upadyaya [
17] also found that personal resources (e.g., employees’ resilience) positively affect work engagement and reduced turnover intentions. Alessandri et al. [
35] noted that personal resources (e.g., hope, resilience, optimism, and efficacy) positively predicted increased work engagement and higher job performance. Gawke et al. [
37] also noted that a positive change in employees’ personal resources over time predicted a higher level of work engagement.
From the literature, we found that not many studies examined both job resources and personal resources in the same structural equation model. Each job resource and personal resource has taken a role as a predictor of work engagement, but many researchers focused on just a single resource when examining the relationship between resources, work engagement, and employee outcomes. However, some researchers examined the effects of those two resources and found that they are closely related. For example, Lorente et al. [
13] found from 228 construction employees’ surveys that personal resources (i.e., self-efficacy, mental and emotional competences) are positively associated with job resources (i.e., job control and supervisor social support), which in turn impact higher work engagement and self-rated performance. Another study conducted by Trépanier et al. [
38] indicated that the personal resource (employee’s harmonious passion) partially mediated the relationship between job resources and work engagement.
Most studies that investigated the effects of job and personal resources on work engagement and employee outcomes relied on survey instruments as the main method of data collection. However, Van Wingerden, Derks and Bakker [
39] investigated the importance of personal and job resources on job performance through work engagement by conducting a quasi-experimental study. They found that using personal resources as an intervention positively affects work engagement. Furthermore, using personal and job resources as an intervention positively impacts employees’ self-rating of their job performance. More studies are needed to examine the effects of both job and personal resources in relationship to work engagement and employee outcomes.
1.4. The Mediating Effects of Work Engagement
Previous literature supported work engagement in a critical role as a mediator between job/personal resources and employees’ job performance and turnover intention. Depending on study contexts and research questions, researchers have examined work engagement with different variables. The majority of studies have used engagement as a mediator [
4,
10,
13,
25,
27,
34,
35,
37,
40,
41]. On the other hand, some studies have shown engagement factors as antecedents [
41,
42,
43,
44,
45] or outcomes [
30,
46,
47,
48,
49,
50,
51,
52].
In this section, we have summarized the literature that specifically uses work engagement as a critical mediator between resources and employee outcomes. Xanthopoulou et al. [
42] found that work engagement played a mediation role in the relationship between self-efficacy and job performance. They also made a note that support and self-efficacy affected performance through work engagement. Recently, Airila et al. [
40] conducted a study using a ten-year longitudinal design to expand the JD-R model by emphasizing long-term effects of job and personal resources on engagement, and consequently on work ability. They found that work engagement fully mediated the influence of job and personal resources on work ability. As a part of employee outcomes, several studies have examined work engagement as a mediator between job / personal resources and turnover intentions. Schaufeli and Bakker [
53] indicated that work engagement mediated between job resources and turnover intention. However, more studies should be conducted to verify those relationships and explore a holistic model by including both personal and job resources when examining the effect of work engagement as a mediator between resources and employee outcomes.
Taken together, we have summarized the main conclusions from the literature review as follows: (1) The basic assumption was made based on SET that people tend to engage in work more actively and produce positive work outcomes when they receive positive support from the job; (2) the previous studies demonstrated the importance of work engagement to employees’ job performance by considering other variables, such as personal resources and job resources even though not many studies examined both personal and job resources in the same model; (3) most previous research on work engagement relied on survey instruments; and (4) the majority of studies have used engagement as a mediator.