The answer is: A shining light from heaven

Acts 9:3-4 - Saul's encounter with a brilliant light was pivotal, marking the beginning of his transformation into Paul, the Apostle. This event emphasizes God's power to change hearts; similar radical transformations occur throughout Scripture, such as Matthew the tax collector (Matthew 9:9). Saul’s journey from persecutor to preacher underscores divine grace and purpose.