The context of this passage is about the conversion of Saul and him being anointed by God's Prophet Samuel as king over Israel. Prior to him being appointed by God through His chosen vessel, a group of prophets informed him that the Lord was going to give him a new heart (1 Samuel 10:5-7). This passage of Scripture is most certainly intriguing, seeing how the language seems to correspond to New Testament text such as 2 Corinthians 5:17.
My personal opinion on the matter is that he was once born again but walked away from his salvation. If that is the case, then we see evidence of the Holy Spirit's regenerating work in the Old Testament. Maybe King Saul came to a point of having saving faith, but chose not to continue in that pursuit. God can use anybody or anything to accomplish His will. This exercise is only meant to provide some food for thought.