What does Galatians 3:15 mean?
In Galatians 3, Paul makes a series of arguments to the Christians in Galatia. He seeks to help them understand why what the Judaizers taught was false. The Judaizers agreed that all should believe in Jesus, but they said we must also continue to follow the works of the law to be truly saved (Galatians 2:4).Paul has attacked that idea from two directions so far. First, he pointed to the Galatians' own personal experience. They received the Holy Spirit after trusting in Christ and before doing any works of the law (Galatians 3:2–5). Why would they think they must be circumcised and start following the law to be saved?
Second, he argued from the Old Testament scriptures that God's Word has always taught that salvation is by faith, starting with the declaration that Abraham was declared righteous—"justified"—for believing the Lord. In fact, following the law reveals that we are all under God's curse for breaking the law. Through faith in Jesus's death in our place, we can all become Abraham's children and be included in God's family (Galatians 3:6–14).
Now Paul begins to argue with the false teaching of Judaizers from a legal standpoint. He asks the Galatians to think about a legal covenant. Probably, Paul is referring to a will: a legal document declaring who receives an inheritance once the person creating the will has died. Under Greek law, a will could not be altered once it was fully completed. Perhaps that's the system to which Paul is referring.
In any case, Paul's readers understand that some contracts, even human ones, cannot be revoked or changed. They are binding no matter what circumstances follow. Paul will show that God's covenant with Abraham was binding still, even after the law was put in place.