Is making a promise to God and then breaking it a mortal sin? It was not broken out of explicit disire to do so but out of reclesness.
Also I realized it and because I was doing something else I thought that I would finish doing it even if I was late. In the end I didn’t do it because it was too late.
I think it would depend on the nature of the promise as well as the reason for not carrying it out.
For example, a priest makes a solemn vow to pray the Divine Office every day. But if they become exhausted after responding to numerous pastoral emergencies and fall asleep in their sitting chair, I think the culpability is limited.
I believe the different types of “promises” to God carry different weight. These are promises which we need to carry out. After all, we gave our word.
Then there are vows, these seem to me to carry more weight than a simple promise. a vow me become a grave matter.
After this come solemn vows and oaths before God. To me, these are serious promises making violating them a grave matter. Thus, to me, it is most likely these carry the weight of mortal sin if they are ignored for other than the most serious of reasons.
In this light, we must also not forget what a moral sin is. It must be a grave matter, you must have a least a brief moment to reflect on it, and after that you must consciously consent to do it.
