Even if his opponents conceded that Abraham’s life was characterized primarily by faith, Paul knew that they still would have questions about why God gave the law to Israel about four centuries after Abraham. Did not the giving of the law nullify any previous arrangement? What is the point of Paul’s analogy between a person’s final will and testament and God’s covenant with Abraham? Gal. 3:15-18
Read more at the source: Sunday: Law and Faith (Gal. 3:15-18)