This sacrament is called Baptism , after the central rite by which it is carried out: to baptize (Greek baptizein ) means to “plunge” or “immerse”; the “plunge” into the water symbolizes the catechumen’s burial into Christ’s death, from which he rises up by resurrection with him, as “a new creature.”
This sacrament is also called " the washing of regeneration and renewal by the Holy Spirit ," for it signifies and actually brings about the birth of water and the Spirit without which no one “can enter the kingdom of God.”
“This bath is called enlightenment , because those who receive this [catechetical] instruction are enlightened in their understanding . . . .” Having received in Baptism the Word, “the true light that enlightens every man,” the person baptized has been “enlightened,” he becomes a “son of light,” indeed, he becomes “light” himself . (CCC)