It is a pleasing custom that brings grace and nature freed from sin, and man, who so longs for cleanness, into the unity of the sign of the cross. At evening also we sign ourselves in holy water. Night, as the proverb says, is no friend to man. Our human nature is formed and fashioned for light. Just before we give ourselves over into the power of sleep and darkness, and the light of day and consciousness is extinguished, there is a satisfaction in making the sign of the cross on ourselves with holy water.
Holy water is the symbol of nature set free from sin.
And at morning, when we emerge again out of sleep, darkness and unconsciousness, and life begins afresh, we do the same thing. But in the morning it is to remind ourselves of that holy water from which we have issued into the light of Christ. The soul redeemed and nature redeemed encounter one another in the sign of the cross.