Homilies on the Epistle to the Hebrews

^5. “For it is impossible for those who were once enlightened and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, and have tasted the good word of God, and the powers of the world to come, if they shall fall away, to renew them again unto repentance, crucifying to themselves the Son of God afresh, and putting Him to an open shame.”

And see how putting them to shame, and forbiddingly he begins. “Impossible.” No longer (he says) expect that which is not possible; (For he said not, It is not seemly, or, It is not expedient, or, It is not lawful, but “impossible,” so as to cast [them] into despair), if you have once been altogether enlightened.