'According to the custom of the feast. In Deuteronomy, Moses commanded the children of Israel: Three times in a year shall all thy males appear before the Lord thy God in the place which he shall choose: in the feast of unleavened bread (the Passover), in the feast of weeks, and in that of tabernacles. No-one shall appear with his hands empty before the Lord, but everyone shall offer according to what he hath, according to the blessing of the Lord his God, which he shall give him. [Dt 16.16-17]

Note that these three solemnities stand for the three states of beginners, proficients and perfect.'

St. Anthony of Padua