The spirit left Saul so did he become unregenerate ?Actually, the regeneration is an old testament concept.
We first see it in the life of Saul. 1 Samuel 10:6
We then see it in the life of David. Psalm 51.
We then see it in each of the prophet's lives. But I think Isaiah 6 is probably the most profound.
Ezekiel describes it in
Although, I think I like 36:25-27 the best. I consider it the most perfect description of the new birth ever provided in such concise terms.
I further think that the only way to see the old testament references of the regeneration is to understand what the new birth is. God may not have used "born again", regeneration, or other new testament terms, but it's clear that everyone with whom God directly interacted in the old testament, they were in fact regenerated.
Eze 36:26 is a future prophesy fulfilled in NT times
In the old testament it was common for the spirit to on or in Kings and prophets but that appears to be for service