Baptism

The sacrament of baptism ushers us into the divine life, cleanses us from sin, and initiates us as members of the Christian community. It is the foundation for the sacramental life. 

"Baptism is the sacrament of faith. But Faith needs the community of believers.
It is only within the faith of the Church that each of the faithful can believe.
The faith required for Baptism is not a perfect and mature faith,
but a beginning that is called to develop."

-Catechism of the Catholic Church
Paragraph 1123