St. Thomas Aquinas
“Since the whole mystery of our salvation is comprised in this sacrament, therefore is it performed with greater solemnity than the other sacraments. And since it is written (Eccles. 4:17): ‘Keep thy foot when thou goest into the house of God’; and (Ecclus. 18:23): ‘Before prayer prepare thy soul,’ therefore the celebration of this mystery is preceded by a certain preparation in order that we may perform worthily that which follows after.”
Source: St. Thomas Aquinas, Summa Theologica