Section 1735 of the catechism lists reasons for which a grave action may not impute culpability in the full sense or even at all, under certain circumstances. Even intentional sins of grave matter may not necessary impute full culpability for the action.
The first condition is inadvertence. If you made the remark inadvertently, you just lost control for a moment, it’s probably not a mortal sin.
No priest has ever asked me about how 1735 applies the sins I confess. The priest has no way of knowing whether they are mortal sins or not. You just go into the confessional, say each sin and the number of times, and get it over. No explaining is needed unless the priest asks a question.
There are examples in the bible … A woman slave is forced into adultery. She is not guilty of the sin. From the cross, Jesus said, Father forgive them for they know not what they do – ignorance of sin reduces the culpability for the sin.
Mental or other social problems. Not much detail here. Maybe a social factor is if a husband forces a wife to have an abortion. She’s not full responsible for that grave action.
1735 sounds technical, but it is about God’s mercy regarding complicated situations where grave matter may be involved.
Lying is not a sin that exists in a vacuum. There are other commands of God, such as to save a life. This is not generally to endorse that the end justifies the means. But, we also have an obligation to save a life if we can.
Jewish moralists rationalize that almost any of the commandments may be broken for a good reason, except several big ones like you can’t deny God or worship false idols; there are others that cannot be compromised, even at the risk of death.
Dt 6:4 You shall love the LORD your God with all your heart, with all your soul, and with all your strength.
The Jewish commentaries have understood that “with all your soul” means even to the point of death. Many of the early martyrs in the Church were not willing to compromise their faith. As revelations says, they did not love their lives so much as to shrink from death.