The writer of the letter of Hebrews exhorts those who had once embraced the new covenant of grace to not drift from it (Hebrews 2:1, 9).
Drifting from grace is drifting back into a religious system, spiritual disciplines, or legalistic church practices as the means for relating to God.
The new covenant of grace in Hebrews is relating to God based solely by faith in the finished work of Jesus.
It is resting in God's complete forgiveness.
It is enjoying fellowship with God 24/7, not because a person confessed all of his sins.