PASSAGE: "For it is impossible to restore again to repentance those who have once been enlightened, and have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, since on their own they are crucifying again the Son of God and are holding him up to contempt" (Hebrews 6:4-6 NRSV).
COMMENT: This passage touches on the important distinction between living in ignorance of spiritual Truth and living in violation of spiritual Truth. If we are ignorant of our own Christ Nature, ignorant of the creative power of our thoughts, we are likely to make many negative choices out of that ignorance. We will experience the negative consequences of those negative choices, because that is how the Law of God expresses. But the consequences will not be as severe as they might be, because that is how the Grace of God expresses.
Once we are awakened to spiritual Truth, however, the game changes. If we now decide to deliberately disregard that Truth and make negative choices based on greed, or lust, or anger, the consequences of those choices will be immediate and severe. This is vividly illustrated in the stories of recovering addicts who, once experienced in the positive energies of recovery, choose out of despair to go back to old addictions. The consequences are much more severe and immediate than before recovery.
In God, however, all things are possible. So I can't fully agree that it is "impossible to restore to repentance those who have once been enlightened." Since we are all fully expressive of the infinite Love that is God, no one can be said to be irretrievable lost. From a human perspective, it is certainly harder to find our way out of the wilderness a second time. But if we reach out, the Love of God will never be denied us.