Galatians 3

The gospel or doctrine of Jesus Christ was taught from the beginning. Yet the Jews continued to fall back believing "the law" or the law of Moses was all that was required for salvation. To which questioned -

" O FOOLISH Galatians, who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you?
2 This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith?" (New Testament | Galatians 3:1 - 2)

Paul then recounts the gospel in the beginning and how the law of Moses came forth. First, Paul recounts that Abraham received the gospel of Jesus Christ by the Spirit, long before the Israelites received the law of Moses teaching -

"Even as Abraham believed God, and it was accounted to him for righteousness.
7 Know ye therefore that they which are of faith, the same are the children of Abraham." (New Testament | Galatians 3:6 - 7)

Being Abraham's children would mean receiving all the blessings of Abraham or "being joint-heirs" with Abraham for -

"So then they which be of faith are blessed with faithful Abraham." (New Testament | Galatians 3:9)

Paul teaches that all the blessings (exaltation) of the covenant with Abraham -

"...might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
15 Brethren, I speak after the manner of men; Though it be but a man's covenant, yet if it be confirmed, no man disannulleth, or addeth thereto.
16 Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ." (New Testament | Galatians 3:14 - 16)

Paul teaches that the covenant made with Abraham could not be broken. Moses came years afterwards and the Lord would not then make a higher law or break the covenant with Abraham such that the law -

"...cannot disannul, that it should make the promise of none effect.
18 For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise." (New Testament | Galatians 3:17 - 18)

Why then was the law of Moses given. Because the Israelites were far from prepared to live according the gospel of Jesus Christ, therefore -

"...the law was our schoolmaster to bring us unto Christ, that we might be justified by faith." (New Testament | Galatians 3:24)

The purpose was that eventually -

"...after that faith is come, we are no longer under a schoolmaster.
26 For ye are all the children of God by faith in Christ Jesus.
27 For as many of you as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
29 And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise." (New Testament | Galatians 3:25 - 29)

Many confuse "law" or Mosaic law with commandments. There are lessor commandments and greater commandents requiring faith in Jesus Christ. That is why -

"Abraham believed God, and it was accounted to him for righteousness." (New Testament | Galatians 3:6)