When you arrive late to Mass, do you commit a sin?
The precept of the Church concerning the Mass says: “The first precept: You shall attend the entire Mass on Sundays and holy days of obligation.” (Catechism n. 2042). “The entire Mass” indicates physical presence and attention. This presence must be continuous, that is, lasting from the beginning to the end of the Mass so that one who omits the most important part of the Mass does not fulfill this precept. In particular:
1) He who omits the consecration (for example going outside), even if they are present the whole time before and after the consecration, does not fulfill the precept.
2) He who arrives after the offertory does not fulfill the precept.
3) He who arrives at the Gospel and also leaves immediately after communion does not fulfill the precept.
In these cases, clearly, I am referring to an absence from Mass without a just cause. It is not the case for the sick person who for one reason or another must leave the Church because of their illness or for parents who have to leave for their children, etc.
In short, this is why, we need to pay more attention to the reason why a person does not attend Mass. It could be that the negligence causing him to be late implies that he has little appreciation for the Holy Sacrifice of the Mass.
Fr. Miguel A Fuentes, IVE