The mysteries of Jesus' infancy
Jesus' circumcision, on the eighth day after his birth, is the sign of his incorporation into Abraham's descendants, into the people of the covenant. It is the sign of his submission to the Law and his deputation to Israel's worship, in which he will participate throughout his life. This sign prefigures that "circumcision of Christ" which is Baptism.
Source: Catechism of the Catholic Church (Vatican.va)