Hebrews 6:4-6

For it is impossible to bring back to repentance those who were once enlightened—those who have experienced the good things of heaven and shared in the Holy Spirit, who have tasted the goodness of the word of God and the power of the age to come— and who then turn away from God. It is impossible to bring such people back to repentance; by rejecting the Son of God, they themselves are nailing him to the cross once again and holding him up to public shame.