Paul continues his argument in this chapter that justification is by faith in God, not merely by obedience to the Law. This argument serves perhaps two causes for Paul:
- Soteriological: to reinforce his point that only obedience to God which is the result of faith (inward circumcision in the language of Deuteronomy) is true obedience, because justification is by faith. Paul wants to emphasise that the promises given to Abraham, the foundation for the great hope of all believers are given to those who have faith and are realised in the New Covenant, not in the Sinaitic Covenant.
- Ecclesiological: to emphasise to the Jewish believers in Rome that the Law was subservient to the true means of justification before God, which is faith. Therefore, Paul can disconnect both circumcision (4:10) and obedience to the Law from justification (4:13, see Galatians 3:17-18). Abraham did not have the Law (contrary to some Rabbinic teaching, which illustrates the problem Paul had!) and so justification cannot rely on the Law. Abraham was justified (his faith reckoned as righteousness) while uncircumcised, so justification cannot rely upon circumcision.
Participation in God's people through justification and becoming a beneficiary of the promises given to Abraham does not depend on circumcision, or on the Law, but on faith in Jesus Christ alone.