Galatians 3: A Synopsis by Stephen T. Kia
This is how I understand Galatians 3. Consider first Hebrews 6:13, which says:
“For when God made the promise to Abraham, since He could swear by no one greater, He swore by Himself…”
Now, realize that Paul is writing to an audience familiar with the nuances of the Law and the Prophets. They would have understood that the Messiah, i.e. Abraham's Seed, would be God-man, because so the prophets foretold (e.g. Isaiah 9:6). We have to read Galatians 3 with that realization in order for it to make sense.
The Law brings a curse, but blessing comes to Abraham's descendants through faith in the God-man, Christ Jesus.
The blessing in question is the promise of the Holy Spirit.
That promise was spoken to Abraham, but it was made to his Seed. In essence, it was made by God to Himself; it was a one-party agreement between God and the God-man, with Abraham as a witness. The God-man would be free to pour out His Spirit (the promise) on all mankind (Joel 2:28).
The Jews mistakenly saw the promise as being made by God to them, Abraham’s seeds. They saw the Law as an amendment to the original promise, a condition added to the covenant 430 years after it was first spoken to Abraham. If they would keep the Law, then the promise would be fulfilled. Paul is saying, "No!" The Law is an entirely separate matter. It has nothing to do with the promise. It was simply a tutor (jump ahead to verse 24) to teach man that God cannot enter into direct relationship with man; because of sin there must be a mediator. Moses was simply a type of the true mediator, the God-man, Christ Jesus. The proof that the Law has nothing to do with the fulfillment of the promise is that the promise involved one party (God and Himself), whereas the Law involves two (God and man). They are two separate matters.
Just because they are two separate matters doesn't mean that they are in conflict with each other. In point of fact, the Law helps point us to the God-man so that we can participate in the blessing of the promise through faith in Him as our mediator. We learned from the Law that we need a mediator, and we find Christ to be the only mediator between God and man (1 Timothy 2:5).
Now we enjoy the fulfillment of the promise, for we have all received the Holy Spirit; we are all "sons of God through faith in Christ Jesus." It was granted to Abraham that the inheritance of the promise to the God-man be enjoyed by his descendants: “in him all the nations of the earth shall be blessed" (Genesis 18:18). “And if you belong to Christ, then you are Abraham’s descendants, heirs according to the promise” (Galatians 3:29).
The whole point Paul is making in the book of Galatians is: grace not works! 2 Corinthians 5:18,19 makes it clear that God was in Himself reconciling the world to Himself. That's what Paul was saying about the promise by God to the God-man. It was a one-party deal. Man had nothing to do with either its conception or its implementation, so that no one could boast (Ephesians 2:8,9). The law, on the other hand, was a two-party deal requiring a mediator. It taught us that we need to come to God on the basis of faith. The practical application of all this is: grace, not works! "Having begun by the Spirit, are you now being perfected by the flesh?" (Galatians 3:3). Sanctification, just like salvation, is an inside-out process by the Holy Spirit, not outside-in by external works of man. As Jesus said, speaking of the Spirit: "He who believes in me...from his innermost being will flow rivers of living water" (John 7:38,39).