Regarding "final perseverance", it can ONLY be a gift. We cannot merit this, but we pray for it, especially in the second half of the "Hail Mary": "Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death. Amen" We address our prayer to divine mercy rather than justice. I suppose the key problem I had was with "absolute" assurance. It is difficult to judge anything as "absolute", especially when we base our religious beliefs on faith - which is, by nature, things not yet seen.
Regards
Of course. It is an error to regard our liturgical work as meriting salvation, -- that would be a form of pelagianism, -- but it is equally an error to say that divine mercy is not moved by pleas for mercy. Let us remember that we do not go to mass to get anything, but rather to simply be at the hill of Golgotha.