Vigilance, and like mental attitudes of heedfulness, wakefulness,and concentration, are necessary for progress on the spiritual path.
Heedfulness is necessary because life is a continuous stream: every moment is an occasion to think, will, and act either within the discipline of the spiritual path or to violate its teachings. Despite one’s initial burst of enthusiasm for the Way, it is all too easy to slip back into fallen and worldly habits. Only continued vigilance can preserve our life.
(from the book: World’s Scriptures II)