God is not obligated to anyone. Everything he does for fallen man is of His Grace, for His Glory alone.
Though doing all to His glory means nothing selfish, or otherwise "as though he needed any thing, seeing he giveth to all life, and breath, and all things; (Acts 17:25) but it means that "He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things?" (Romans 8:32)
And salvation by grace, for man could not and would not believe on the Lord Jesus or follow Him unless God gave him life, and breath, and all good things he has, (Acts 17:25) and convicted him, (Jn. 16:8) drew him, (Jn. 6:44; 12:32) opened his heart, (Acts 16:14) and granted repentance (Acts 11:18) and gave faith, (Eph. 2:8,9) and then worked in him both to will and to do of His good pleasure the works He commands them to do. (Phil. 2:13; Eph. 2:10)
But which works, resulting from faith, do not appropriate justification, but as saving faith is that which effects obedience, this fruit justifies one as being a believer, with "things that accompany salvation." (Hebrews 6:9)
Thus man owes to God all things, even the ability and motivation to obey Him, and in justice man only actually deserves damnation, since what man must take credit for for is resisting God, whatever the level of grace given him is. (Prov. 1:20-31; Lk. 10:13; 12:48; Rv. 20:11-15) Yet under grace, which denotes unmerited favor, God has chosen to reward faith, (Heb. 10:35) in recognition of its effects, which God is actually to be credited for.
Which thus means that God justifies man as one "accepted in the Beloved" (Eph. 1:6) not on the basis that his works merit this, and which is what Romans 4:1-7ff teaches, with works of the law including all systems of this justification by the actual merit of works, for, "if there had been a law given which could have given life, verily righteousness should have been by the law." (Galatians 3:21)