Before Acts 9 can you give me scriptures that shows the twelve apostles teaching that we are not under the law, there is no difference between Jews and Gentiles, and that we are saved by grace through faith in the death and resurrection of Christ only for salvation? I can't find it prior to Paul, but if you can I'd love to.
What you are doing is restricting the possibilities in order to say that Paul somehow changed Christianity. Yes, Paul's conversion is mentioned in Acts 9, but he did not meet Peter until three years after his conversion. "But when God, who had set me apart even from my mother's womb and called me through His grace, was pleased to reveal His Son in me so that I might preach Him among the Gentiles, I did not immediately consult with flesh and blood, nor did I go up to Jerusalem to those who were apostles before me; but I went away to Arabia, and returned once more to Damascus. Then three years later I went up to Jerusalem to become acquainted with Cephas, and stayed with him fifteen days. But I did not see any other of the apostles except James, the Lord's brother" (Galatians 1:15-19). Even when they did meet, fifteen days would not have been long enough to change Peter's teachings. Thus, the events in Acts 10 took place before Peter and Paul met. It was Peter who stated, "I most certainly understand now that God is not one to show partiality, but in every nation the man who fears Him and does what is right is welcome to Him" (Acts 10:34-35).
Prior to this, Stephen was arrested "for we have heard him say that this Nazarene, Jesus, will destroy this place and alter the customs which Moses handed down to us" (Acts 6:14). We don't have exactly what Stephen said, but it did lead the Jews to conclude that Stephen was teaching a change in the law. Stephen wasn't one of the twelve apostles, but he was a leading man in the church and a man inspired by the Holy Spirit.
Prior to Stephen, Peter quoted, "And in your seed all the families of the earth shall be blessed" (Acts 3:25) and applied this quote to Jesus. "All the families of the earth" would mean that Jews and Gentiles would be treated equally in this blessing. Earlier, in his first sermon, Peter stated, "Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit. For the promise is for you and your children and for all who are far off, as many as the Lord our God will call to Himself" (Acts 2:38-39). "All who are far off" is also a reference to the Gentiles, indicating that they would receive salvation equally with the Jews.
This should not be surprising since Jesus told his disciples, prior to his departure from earth, "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, teaching them to observe all that I commanded you" (Matthew 28:19-20). The apostles, long before Paul was converted were commanded to make disciples of all nations and to teach them equally. Jesus also talked about the saving of the Gentiles earlier in his ministry, "I have other sheep, which are not of this fold; I must bring them also, and they will hear My voice; and they will become one flock with one shepherd" (John 10:16). The other sheep was a reference to the Gentiles who would become Christians. The equality is again shown because they would become one flock under one shepherd (Jesus) (Ephesians 2:11-18-22). It was also Jesus to taught that salvation would only be available through him. "Jesus said to him, 'I am the way, and the truth, and the life; no one comes to the Father but through Me'" (John 14:6).
But long before any of this God prophecied that this would happen. Speaking of the task of the Messiah, "He says, 'It is too small a thing that You should be My Servant to raise up the tribes of Jacob and to restore the preserved ones of Israel; I will also make You a light of the nations so that My salvation may reach to the end of the earth'" (Isaiah 49:6). Saving just the Jews would be too minor of a task for the Son of God. He came to save the world.
God also foretold the changing of the Law. "'Behold, days are coming,' declares the LORD, 'when I will make a new covenant with the house of Israel and with the house of Judah, not like the covenant which I made with their fathers in the day I took them by the hand to bring them out of the land of Egypt, My covenant which they broke, although I was a husband to them,' declares the LORD. But this is the covenant which I will make with the house of Israel after those days," declares the LORD, 'I will put My law within them and on their heart I will write it; and I will be their God, and they shall be My people'" (Jeremiah 31:31-33).
Are any of these worded the way Paul stated them? No, but it doesn't mean it wasn't taught or that Paul somehow changed God's religion. Paul taught what Jesus wanted to be taught and what Jesus had taught while he was here on earth.