The Jews believed that they had a claim on Abraham that Gentiles did not have. Obviously he was the father of their nation, and this did place him in a unique relationship to his physical descendants. However, they incorrectly concluded that all the blessings that God had promised Abraham would come to them. Paul reminded his readers that part of God's promised blessing to Abraham was that he would be the father of many nations (v. 17). God had given him this promise after his justification (Gen. 17:4-6), and He repeated it to his descendants (Gen. 22:17-18).
4:13 God gave His promise to bless the Gentiles through Abraham long before He gave the Mosaic Law. Consequently it was wrong for the Jews to think that the blessing of the Gentiles depended on their obedience to the Law. It depended on God's faithfulness to His promise. God gave that promise to Abraham not because of his obedience but because of his faith. The giving of that promise even antedated Abraham's circumcision.
4:14 To introduce law-keeping as a condition for the fulfillment of this promise would have two effects. First, it would make faith irrelevant. It would subject this simple unconditional promise to the condition of human obedience. If, for example, a father promised his son a new bicycle, the boy would look forward to receiving it as a gift. However if the father added the condition that to get the bike the boy had to be obedient, he would destroy his son's confidence that he would get the bike. Now obtaining the bicycle depended on obedience. It was no longer a matter of faith. The second effect, which is also evident in this illustration, is that the promise would be nullified (i.e., made worthless).
4:15 Rather than bringing blessing, which God promised Abraham, the Law brings wrath because no one can keep the Law perfectly. Whenever there is failure, wrath follows. However without law there can be no violation and therefore no wrath.
"Violation of law turns sin' into the more serious offense of transgression,' meriting God's wrath
God gave the law to the Jews
The Jews have transgressed the law (cf. 2:1-29; 3:9-19)
The law brought wrath to the Jews . . .
"Paul, then, is not claiming that there is no sin' where there is no law, but, in almost a truism,' that there is no deliberate disobedience of positive commands where there is no positive command to disobey."134
4:16 This verse summarizes the thought of verses 13-15. God gave His promise to make Abraham the father of many nations (v. 13) unconditionally ("in accordance with grace") after the patriarch stood justified. Abraham obtained the promise simply by believing it (i.e., by faith), not by keeping the law. This is the only way that the realization of what God had promised could be certain. This part of Paul's argument therefore further exalts faith as the only method of justification.135
"Faith is helplessness reaching out in total dependence upon God."136
4:17 Paul described God as He did here in harmony with the promise he cited. God gave the ability to father many nations to Abraham when he was already dead regarding his reproductive powers. God summoned yet uncreated nations as He had summoned the yet uncreated cosmos, namely with a word, in this case a promise (cf. Heb. 11:3; 2 Pet. 3:5).137
