Galatians 3:15-18…16 Now the promises were spoken to Abraham and to his seed. He does not say, “And to seeds,” as referring to many, but rather to one, “And to your seed,” that is, Christ.
Paul inspired by the Holy Spirit tells us in v.15 that contracts between humans that have been signed contain firm business details and that no changes are made to the contract unless agreed to by both parties to the contract. A covenant is an agreement between people about their own relationships such as a marriage covenant. The marriage covenant also involves a third party, God, for Disciples. This covenant agreed to before God cannot be changed, but in extreme cases can be broken through divorce. This always results in damage to many people and especially if there are children of the marriage.
V.16 refers to the promises made to Abraham A that includes the promise of descendants, a land, the covenant of grace would be eternal and his seed would bless all the nations. We are told in v.16 the Jesus Christ is the seed promised. Each Disciple today is a spiritual descendant of Abraham through Jesus.
The Law came 430 years later and vv.17-18 tells us this Law did not nullify the eternal covenant and promise previously made to Abraham by God. The inheritance promised to Abraham was based on the promise and covenant, not the subsequent Law.
We can be thankful to God for His faithfulness to the promise He made to Abraham 4,000 years ago and the fulfillment by sending His Son Jesus Christ to earth to die for our sins. The final fulfillment will come when He returns with His saints and defeats Satan and then places Satan in the lake of fire forever.
Notes: A- The promise made to Abraham is in Genesis 12:3,7;13:15-16;15:5;17:7-8;21:12; 22:17-18 v.16 above is from Genesis 22:17-18;