The Lord never changed Paul’s name. “Paul” is his Roman name. “Saul” is his Hebrew name.
In Acts 13, the Church in Antioch set up the first mission among the Gentiles.
Acts: 13:2-3 - While they were worshiping the Lord and fasting, the holy Spirit said, "Set apart for me Barnabas and Saul for the work to which I have called them."Then, completing their fasting and prayer, they laid hands on them and sent them off.
It seems that the name “Paul” works better among the Gentiles than the thoroughly Jewish name of “Saul”. That may be the reason he uses it from then on. From then on, he’ll go by the name of Paul.
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