Nothing seemed sacred to Saul even he was anointed king & knew of God.
To send three lots of men & then go his-self when he heard they were all prophesing, then to acctually prophesy as well, he still had no regard for God at all.
God is all powerful,it seems whenever the the Holy Spirit comes upon people, they start prophesying, in Sauls time & also at pentecost; it is the power of God, we may not understand it, there are many things I do not understand, but just to have faith & trust in God in all things.
The Holy Spirit came on the day of pentecost, Jesus told his disciples to stay in the upper room & wait, then the Holy Spirit came upon them, they prophesied & spoke in tounges.