Masses on Holy Days of Obligation like this past Saturday—the Solemnity of the Immaculate Conception —are obligatory by Cannon Law and the teaching of the Catechism. This obligation makes the subject of Mass attendance on these occasions a serious or grave matter. The Catechism of the Catholic Church speaks of the distinction between mortal and venial sin in numbers 1855-1864. It defines mortal sin in 1857:
“For a sin to be mortal, three conditions must together be met: “Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent.” That basically means that when we are able to go to Mass and choose not to, we commit a mortal sin. Numbers 1020-1041 of the Catechism speak of what are known as the “Last Four Things.”: i.e. Death, Judgement, Heaven and Hell. Number 1033 says the following: “We cannot be united with God unless we freely choose to love him. But we cannot love God if we sin gravely against him, against our neighbor or against ourselves: “He who does not love remains in death. Anyone who hates his brother is a murderer, and you know that no murderer has eternal life abiding in him.”
Our Lord warns us that we shall be separated from him if we fail to meet the serious needs of the poor and the little ones who are his brethren.613 To die in mortal sin without repenting and accepting God’s merciful love means remaining separated from him for ever by our own free choice. This state of definitive self-exclusion from communion with God and the blessed is called “hell.” My vocation to the priesthood and my calling to serve this parish is essentially for the salvation of your souls. It deeply pains me to see how many take their serious obligation to Mass attendance so lightly. You will never regret putting God first in your life.