Hebrews 6:1-6

Therefore let us get past the elementary stage in the teachings about the Christ, advancing on to maturity and perfection and spiritual completeness, [doing this] without laying again a foundation of repentance from dead works and of faith toward God, of teaching about washings (ritual purifications), the laying on of hands, the resurrection of the dead, and eternal judgment. [These are all important matters in which you should have been proficient long ago.] And we will do this [that is, proceed to maturity], if God permits. For [it is impossible to restore to repentance] those who have once been enlightened [spiritually] and who have tasted and consciously experienced the heavenly gift and have shared in the Holy Spirit, and have tasted and consciously experienced the good word of God and the powers of the age (world) to come, and then have fallen away—it is impossible to bring them back again to repentance, since they again nail the Son of God on the cross [for as far as they are concerned, they are treating the death of Christ as if they were not saved by it], and are holding Him up again to public disgrace.