The gathering of the People of God begins with Baptism; a church must have a place for the celebration of Baptism (baptistry) and for fostering remembrance of the baptismal promises (holy water font).
The renewal of the baptismal life requires penance. A church, then, must lend itself to the expression of repentance and the reception of forgiveness, which requires an appropriate place to receive penitents.
A church must also be a space that invites us to the recollection and silent prayer that extend and internalize the great prayer of the Eucharist.
Source: Catechism of the Catholic Church (Vatican.va)