Saul is changed greatly, and they are baffled by the change. They see him prophesying, and it appears to be genuine prophecy (although the word may signify the act of worshipping) and he is in the company of the other prophets.
The unbelieving world finds it hard to acknowledge the truth of genuine conversion. It is a mystery to them that anyone can really change. They believe that character is for the most part fixed, and so they do not readily accept that God can create a new nature in a man. Usually this is right, but it does not take account of the saving work of the Spirit in a heart. For this reason, when a person is genuinely converted, it is all the more astounding to the world. Here is someone they knew well, and there were deep seated corruptions in that person, and sinful habits that could never be broken. And yet this person claims to have repented and trusted in Christ for salvation. Nothing but a genuine change which is sustained over time will convince them of this miracle of grace. But in Saul’s case the people were right to be sceptical.