Acts 10:44-48 :

While Peter was still speaking these words, the Holy Spirit fell on all those who heard the word. They of the circumcision who believed were amazed, as many as came with Peter, because the gift of the Holy Spirit was also poured out on the Gentiles. For they heard them speaking in other languages and magnifying God.

Then Peter answered, “Can any man forbid the water, that these who have received the Holy Spirit as well as we should not be baptized?” He commanded them to be baptized in the name of Jesus Christ. Then they asked him to stay some days.

This was a surprising event to the Jewish believers. Up to this point, the Holy Spirit had only filled those who had been outwardly recognized as Jews with the exception of the Samaritans and the man from Ethiopia. This was a large outpouring of the Holy Spirit that happened in the same way as it happened to the Jews on Pentecost.

This was an undeniable sign that things were very different between God and the Gentiles now. No longer did a person have to convert to Judaism to become right with God. There were still some who doubted this at this point, but God was revealing the truth by His actions.

Notice, also, that the Holy Spirit was given before the people were baptized with water. This is yet another proof that baptism isn’t required for salvation. The Holy Spirit is, however, and Peter recognized that they already had the Holy Spirit. So, he figured that there wasn’t anything to doubt about whether or not it was Ok to give them water baptism. The ramifications of this change of “rules” would continue to this very day and the Bible has much more to say about this.

God now relates to mankind in a different way than He did under law of Moses and we can see from other passages that this was God’s plan all along.