One of the questions that arises in the continual debate about how God interacts with man is whether or not all of God's engagement with man involves "grace". In "Covenant Theology Under Attack", Meredith Kline takes on critics of Christ's meritorious work by pointing to one of the passages in which "justice" is the overriding principle governing God's interaction with man:
“Instructive for the concept of justice is the parable of the workers in the vineyard (Matt. 20:1-16). In particular, it illustrates the point that in administering a work contract, the amount of the stipulated wages is irrelevant to the question of justice. Those who worked the full day challenge the owner of the vineyard when they discover that the same pay they received was given to others who labored fewer hours. But they were rebuffed by the reminder that their employer had dealt with them exactly as their work covenant prescribed. To honor the covenant commitment was justice. Similarly, the higher rate of pay received by the others did not transform that transaction into one of "grace." It too was a payment of what was "right" (v. 4). It was simple justice, no more, nothing other than justice.
“…The rewarding of obedience is not something done only in an employer-employee relationship. It takes place in the parent-child relationship too, among others. When the parent promises the child a reward for doing some chore, that is tantamount to a covenant of works, and it is a matter of simple justice that the obedient child receive the covenanted reward. So the doctrine of the Covenant of Works is not necessarily founded on the metaphor of God as an employer. The covenant-keeping parent is another option. The king conferring a royal grant on a loyal subject would be another.
“But actually there is no need to refrain from likening God to an employer. This metaphor…was used by Jesus himself in the parable of the vineyard workers (and other parables). As the example of Jesus' parable demonstrates, metaphors must not be pressed too far and, more specifically, used of the employer metaphor for God does not imply that God, like human employers, is a needy client lord dependent on his employees' services. What we can properly gather from that parable with its employer metaphor is that the God-man relationship is governed by the principle of divine justice, including its positive expression in God's granting covenanted rewards for the performance of stipulated duties. The propriety of the Covenant of Works doctrine is thereby confirmed.
“The ultimate refutation of (non-meritorious) theology is that it undermines the gospel of grace. All the arguments…to prove that Adam could not do anything meritorious would apply equally to the case of Jesus, the second Adam. Thus, the Father was already all-glorious before the Son undertook his messianic mission, and their covenanting with one another took place, of course, within a father-son relationship. Moreover, the parallel which Scripture tells us exists between the two Adams would require the conclusion that if the first Adam could not earn anything, neither could the second. But, if the obedience of Jesus has no meritorious value, the foundation of the gospel is gone. If Jesus' passive obedience has no merit, there has been no satisfaction made for our sins. If Jesus' active obedience has no merit, there is no righteous accomplishment to be imputed to us. There is then no justification-glorification for us to receive as a gift of grace by faith alone.” -- Meredith Kline, "Covenant Theology Under Attack"
A passage that Kline does not employ here (no pun, o-k, pun intended), but could is a well-known passage that has implications many rarely consider in this question. Romans 6:23 uses the employer-employee metaphor when it says that the *wages* of sin is death. Wages are earned. Adam earned death in his sin. But… because wages are earned, the idea of “earned” must also be equally employed for the alternative. The wages of “not sinning” is life. In fact, if we follow Paul’s parallel in this passage between “death” and “eternal life”, we can say that the wages of “not sinning” is eternal life.
That this passage goes on to say that “the free gift of God is eternal life in Christ Jesus our Lord” should not tempt us into thinking the idea of “wages” does not also apply to the opposite of death. Within the parallel of death and eternal life in this passage there is a shift from God dealing with man via “simple justice” to “grace”. Why does Paul say that eternal life is a “free gift” rather than “the wages of not sinning”? Because he has already informed us that it is impossible for anyone to “not sin” (Romans 3:10,23). If we are to have any hope of enjoying the eternal life that Adam failed to earn, it will come to us by grace. Our wages are always death for us, because it is impossible for us to “not sin”.
But the fact that eternal life is God’s gracious gift to us through Jesus Christ does not negate what would be true *if* it was possible for us to “not sin”. Eternal life would be earned (which Paul affirms in Romans 10:5 and Galatians 3:12). And this is precisely what Christ has done for us. For Christ, the wages of “not sinning” was justification and eternal life for His people (Romans 5:18). Without Christ’s earning the wages of “not sinning”, many can not be “made righteous” (Romans 5:19) and there is no grace to “reign through righteousness leading to eternal life through Jesus Christ our Lord.” (Romans 5:21) -- crb