The word (grace) has abundant use in secular Greek in the sense of unmerited favor, and Paul seized on this meaning of the word to express a fundamental characteristic of Christianity. The basic passage is Rom_11:5, Rom_11:6, where as a definition is given, "If it is by grace, it is no more of works: otherwise grace is no more grace." That the word is used in other senses could have caused no 1st-century reader to miss the meaning, which, indeed, is unmistakable. "Grace" in this sense is an attitude on God's part that proceeds entirely from within Himself, and that IS CONDITIONED IN NO WAY by anything in the objects of His favor. So in Rom_4:4. IF salvation is given on the basis of what a man has done, THEN salvation is given by God as the payment of a debt. But when faith is reckoned for what it is not, i.e. righteousness, there is no claim on man's part, and he receives as a pure gift something that he has not earned. (It is quite true that faith involves moral effort, and so may be thought of as a sort of a "work"; it is quite true that faith does something as a preparation for receiving God's further gifts. But it simply clouds the exegetical issue to bring in these ideas here, as they certainly were not present in Paul's mind when the verses were being written.) "Grace" then, in this sense is the antinomy to "works" or to "law"; it has a special relation to the guilt of sin (Rom_5:20; Rom_6:1), and has almost exactly the same sense as "mercy." Indeed, "grace" here differs from "mercy" chiefly in connoting eager love as the source of the act. See JUSTIFICATION. Of course it is this sense of grace that dominates Rom 3 through 6, especially in thesis Rom_3:24, while the same use is found in Gal_2:21; Eph_2:5, Eph_2:8; 2Ti_1:9. The same strict sense underlies Gal_1:6 and is found, less sharply formulated, in Tit_3:5-7. (Gal_5:4 is perhaps different.) Outside of Paul's writings, his definition of the word seems to be adopted in Joh_1:17; Act_15:11; Heb_13:9, while a perversion of this definition in the direction of antinomianism is the subject of the invective in Jud_1:4. And, of course, it is from the word in this technical Pauline sense that an elaborate Protestant doctrine of grace has been developed. (ISBE)
DHK