John Calvin Commentary Galatians 3:14

"that upon the Gentiles might come the blessing of Abraham in Christ Jesus; that we might receive the promise of the Spirit through faith." — Galatians 3:14 (ASV)

That the blessing of Abraham. Having said that Christ hath redeemed us from the curse of the law, he now applies that statement more closely to his purpose. The promised blessing of Abraham is founded on this, and flows from it to the Gentiles. If the Jews must be delivered from the law, in order to become the heirs of Abraham, what will hinder the Gentiles from obtaining the same benefit? And if that blessing is found in Christ alone, it is faith in Christ which alone brings it into our possession.

The promise of the Spirit appears to me to mean, according to a Hebrew idiom, a spiritual promise. Although that promise relates to the New Testament, I will pour out my Spirit upon all flesh, (Joel 2:28), yet, in this passage, Paul refers to another subject. The spirit is here contrasted with all outward things, not with ceremonies merely, but with lineal descent, so as to leave no room for diversity of rank. From the nature of the promise, he proves that Jews do not differ at all from Gentiles; because, if it is spiritual, it is received by faith alone.