Since I've entered the Catholic (or Apostate) Communion I've not posted alot on theology because I've realized how little I understand or know about Catholic theology. Most of my ideas are still Reformed or Evangelical and I feel like the only way to describe it is Chesterton's line in his book on Conversion and the Catholic Church where he says that when you walk into the Church you realize that it's much bigger on the inside, that it's gigantic. I had to face the fact that I might not actually ever fully comprehend my religion. Anyway, I figured since Merit is a topic I knew almost nothing about, I'd try to understand it.
Here are the sources I stole my info from:
Nothing I write is 'magesterial' or anything, I'm just a lay Catholic trying to understand this.
Catholic Teaching on Justification and Merit
Catholic Theology has always taught and always will teach what it has since the Augustine-Pelagian controversy, that man is freely justified by God's grace which is unmeritted and that without this grace it is impossible to do good works which either merit eternal rewards or one's salvation. Merit comes after the application of Justification (baptism in infants, faith and/or baptism in adults, priestly absolution for those in a state of mortal sin). But the tricky thing one must remember when studying Catholic theology is that they believe everything is by grace, but it's resistible grace (think Wesley and everyone Calvin was against) meaning that theoretically God could be beaming down grace to me in every decision I make, but I could still reject it 100 times before I accept it once. The thing to remember also is that much of Catholic theology does not constantly repeat the premiss that grace comes first and is unmeritted. It's kind of a given in Western Christendom.
Types of Merit
I'll use myself as an example. So for me, a recently absolved, baptized, and faithful Catholic who has definately committed venial sins this week, but is still in a state of grace, there are two kinds of merit I could achieve.
1) Congruent Merit
Congruent Merit would be like if I was really hungry and wanted all the perogies in the fridge but then presumably God gave me the grace to tell my cousin she could have some and her then consuming said perogies and thanking me. Now I've done a virtuous thing not out of obligation and not of absolutely pure motive, but because it was prompted by grace and was an act of Christian charity, presumably God would consider it meritous, pleasing, and if he is feeling merciful on judgment day, he will give me a gold star or remove a day from my millenia in Purgatory. Congruent merit isn't as certain, it's more just the hope that God will look on all the good things I did by his grace and because of his graciousness and mercy he will reward me.
2) Condign Merit
Condign Merit would be a much bigger thing. Imagine while my cousin was enjoying the perogies a robber burst in and was going to kill my cousin, and I suddenly was zapped by God's grace and was filled with absolute compassion and sacrificial love and I died protecting my cousin from this evil murderous robber. That would be an act that kind of earns a real reward from God. To use a biblical example, St. James states that those who persevere under temptation will recieve from God a crown of life, or in Revelation when the Martyrs are given crowns, etc.
This is my basic understanding.