a. in repentance for your sins;
b. for protection against the Evil One;
c. to remind you of your baptism.
a. Holy water reminds us to be sorry for our sins. When there is the rite of sprinkling in the liturgy, we always sing the Asperges, which means "you will sprinkle or wash". Asperges me hysoppo et mundabor; lavabis me et super nivem dealbabor. These are words from the great penitential psalm, Ps 50: You will sprinkle me with hyssop and I shall be cleansed: you will wash me, and I shall be made whiter than snow.
b. Holy water is a sacramental which is a protection against the snares of the devil. The old prayer for the blessing of holy water said: "O God, creator of unconquered power, King of invincible empire and victor ever-great: who put down the powers of hostile dominion and conquer the fury of the roaring enemy, who fight powerfully against our wicked foes: trembling we beseech you, O Lord, we implore you and beg you: that you might graciously look upon this creature of water and salt, kindly illumine it, sanctify it with the dew of your loving kindness, so that wherever it is sprinkled, through the invocation of your holy Name, every infestation of the unclean spirit be cast out, and the terror of the poisonous serpent be driven far away. And may the presence of the Holy Spirit deign to be with us always, we who implore your mercy."
c. Holy water reminds us of our baptism: of that great day when we ourselves or our parents or sponsors—renounced Satan, professed faith in Christ, and were baptized into the mystery of the Holy Trinity. At that moment all our sins were forgiven: original and actual, and we became children of God, filii in Filio, heirs of the promise, daring now to call God our Father.When you dip your hand into the holy water font, remember these things, and like Our Lady, treasure them in your heart.