The first mention of Saul’s name change to Paul is in Acts 13:9, “Then Saul, who also is called Paul, filled with the Holy Spirit, looked intently at him.” He is always called Paul thereafter. The Scriptures do not explain how or why Saul’s name was changed, only that he became known as Paul.
Saul’s parents probably named him after the greatest Benjaminite king, Saul. Thus, “Saul” would have been a reference to greatness. Additionally, “Saul” is Strong’s Greek work G4569 from the Hebrew word H7586, meaning “desired.”
“Paul” is Strong’s Greek word G3972 which means “little.” The Apostle doubtless knew Proverbs 3:34 (NET), “Although he (God) is scornful to arrogant scoffers, yet he shows favor to the humble.” Also, the Apostle James wrote, “God opposes the proud, but gives grace to the humble,” James 4:6. It may be reasonable to think that Paul preferred to be called “little” due to his recognition of his humble or lowly status before God.