3 This is in truth a serious matter, brethren, and you must approach it with good heed. Each one of you is about to be presented to God before tens of thousands of the Angelic Hosts: the Holy Ghost is about to seal your souls: you are to be enrolled in the army of the Great King. Therefore make you ready, and equip yourselves, by putting on I mean, not bright apparel, but piety of soul with a good conscience. Regard not the Laver as simple water, but rather regard the spiritual grace that is given with the water. For just as the offerings brought to the heathen altars, though simple in their nature, become defiled by the invocation of the idols, so contrariwise the simple water having received the invocation of the Holy Ghost, and of Christ, and of the Father, acquires a new power of holiness.
Source: Catechetical Lectures (New Advent)