Now the promises were spoken to Abraham and to his seed. He does not say “and to seeds,” as though referring to many, but referring to one, and to your seed, who is Christ. – Galatians 3:16
It appears from Paul’s letter to the church at Galatia that they were being drawn back into an old covenant approach that ran counter to the new covenant message that Jesus had established (and Paul preached). Paul’s clear counter-message was simple, “We are saved by grace through faith alone; not by works.” A new non-Jewish (Gentile) believer was not required to keep any part of the Law in order to become a Christ-follower.
To make his point clearer, Paul referenced Abraham (Israel’s covenant hope) who had received his promise from God 430 years before the law was ever given to Moses on Mt. Sinai. In other words, God reckoned Abraham’s faith as righteousness, not his works, and God honors all the covenants He makes.
Now, if Abraham’s covenant was based on faith, then what about ours? Well, Christ, as the “seed of Abraham” is our Covenant-keeper and He completely fulfilled every requirement that the Mosaic Law set forth when He sacrificed Himself. Now, by believing the gospel (that He died and rose again for your law-breaking attitudes and actions), Jesus’ work on the cross and intercession in heaven satisfies God’s requirements for your own holiness forever.
Were I asked to focus the New Testament message in three words, my proposal would be “adoption through propitiation,” and I do not expect ever to meet a richer or more pregnant summary of the gospel than that. – J. I. Packer