How often have we made the sign of the Cross and invoked the name of the triune God without thinking about what we were doing?  In its original meaning, each time we perform this action, our baptism is renewed.  We take on our lips the words through which we were made Christians, and we consciously accept into our personal life something that was bestowed on us in baptism without any active contribution or reflection on our part.  On that occasion, water was poured over us, and the following words were spoken: "I baptize you in the name of the Father and of the Son and of the Holy Spirit."  The Church makes a man a Christian by pronouncing the  name of the triune God.  In this way, she expressed since the very beginning what she considers the most decisive element of the Christian existence, namely, faith in the triune God.

The God of Jesus Christ by Joseph Ratzinger (Pope Benedict XVI)