So I said, ‘Who are You, Lord?’ And He said, ‘I am Jesus, whom you are persecuting

Acts 26:15
So I said, ‘Who are You, Lord?’ And He said, ‘I am Jesus, whom you are persecuting.

Paul, when he was Saul, was seriously persecuting the followers of Yshua. We may not know fully what the persecution involved but it was very likely to include a lot of violence towards the persecuted. One example was that Saul was presiding, probably instigating the stoning of Stephen - the first to die for our Lord.

Obviously Saul had not physically harmed Yshua, as far as we know. But his actions are regarded as being done on our Lord, when he persecuted His children. Putting aside modern day persecution of Christians by other groups, Christians too may be persecuting each other knowingly or otherwise. If we are not careful of what we say or how we "wear our Christianity" we could be offending the younger Christians, and by doing so we may be persecuting our Lord too.

Luke 17:2
It would be better for him if a millstone were hung around his neck, and he were thrown into the sea, than that he should offend one of these little ones.

Matthew 18:6
“Whoever causes one of these little ones who believe in Me to sin, it would be better for him if a millstone were hung around his neck, and he were drowned in the depth of the sea.