As to the relation of good works to rewards, it may be observed—(1.) The word merit, in the strict sense of the term, means that common quality of all actions or services to which a reward is due in strict justice on account of their intrinsic value or worthiness. It is evident that, in this strict sense, no work of any creature can in itself merit any reward from God, because (a) all the faculties he possesses were originally granted and are continuously sustained by God, so that he is already so far in debt to God that he can never bring God in debt to him. (b.) Nothing the creature can do can be a just equivalent for the incomparable favour of God and its consequences.
There is another sense of the word, however, in which it may be affirmed that if Adam had in his original probation yielded the obedience required, he would have “merited” the reward conditioned upon it, not because of the intrinsic value of that obedience, but because of the terms of the covenant which God had graciously condescended to form with him. By nature, the creature owed the Creator obedience, while the Creator owed the creature nothing. But by covenant the Creator voluntarily bound himself to owe the creature eternal life, upon the condition of perfect obedience.
—Archibald Alexander Hodge, A Commentary on the Confession of Faith (Philadelphia: Presbyterian Board of Publication and Sabbath-School Work, 1869), 307–08.