Roman Catechism 18.133

Chapter 18 — Part II: The Sacraments — The Holy Eucharist

Section 133. Necessity Of Previous Preparation For Communion — We now come to point out the manner in which the faithful should be previously prepared for sacramental Communion. To demonstrate the great necessity of this previous preparation, the example of the Saviour should be adduced. Before He gave to His Apostles the Sacrament of His precious body and blood, although they were already clean, He washed their feet to show that we must use extreme diligence before Holy Communion in order to approach it with the greatest purity and innocence of soul.