I was chatting with an evangelical protestant friend a while back and (I can't remember what I'd said to provoke it) he suddenly commented: 'Careful: that sounds like you can be meritorious!'
He said it in that jokey way we use when we correct someone who we know has used a turn of phrase that is inadvertently heretical. It didn't occur to him that I might think any action of a mere human could have merit, in the sense of contributing to his salvation. That was such a basic error, in his mind, that it was unthinkable that someone halfway intelligent could believe it.
For he has been brought up on the doctrine of Sola Fide - one of the great battle cries of the Reformation.
And why was it a battle cry? Precisely because Catholic teaching was, is, and ever shall be that in fact we can contribute to our own and others' salvation: we can perform actions of real merit. This Luther reacted against: even to the extent of altering the Bible (adding the word alone where St Paul says we are saved by Faith); and condemning the Epistle of St james as an Epistle of Straw!
Of course we are saved by Faith - but not by Faith alone. Without Charity, for example, we are lost. The Catholic belief is that we are saved by grace alone: everything is a gift from God. But one of His gifts is the honour and dignity of being able to cooperate with Him in our salvation, and in that of others.
The principle way in which we do this is by the offering of the sacrifice of the Mass, both for the living and the dead: this was at the heart of what Luther and subsequent Protestantism attack. Their Communion Services are explicitly of no merit: which is one of the many reasons why until very recently Catholics were not permitted to attend them: a discipline I believe could usefully be reinstated.
Sola Fide is strangely unBiblical: try to think how many times Our Lord points out that it is what we do (give these little ones a drink in my name) not just what we profess ('many shall say to me Lord, Lord...') that gains us entry to the kingdom of Heaven...