To the OP: as has been mentioned, the act of committing a mortal sin is not God rejecting us, but us rejecting God. God still loves us as much as ever, but since a relationship is a two way thing and we have killed our part, it is dead. But again, God’s love for us is unchanging (otherwise it would be impossible for the relationship to be restored).
Since God loves us and hears everything we think and say, it would be hard to say that He would just ignore our prayers. It may be that there is a defect in any prayers that we say arising from our rejection of God’s sanctifying grace, but God still hears them and will act as He sees fit.
I’ve tried to find something official somewhere saying that prayers become useless while in a state of mortal sin. I failed. Is there some source for this idea I could read over?
I’ll let someone more qualified answer the finer points, but here’s the basics: if you are truly of a contrite heart and really seek forgiveness, it is already given to you. Go to confession still.
Now I don’t fully understand the why, here, and that’s why I’m waiting for someone a bit more knowledgeable. Why, if you are already forgiven, the confession step is necessary. But it is, and I know that much.
I’m not qualified, but this is the internet, so here goes: Confession doesn’t exist for God. It exists for us. God doesn’t need us to go to confession to forgive us. He instituted the sacrament because, while absolution is obviously the most important result, there are other goods as well. There is something about having to admit out loud to another human (especially one who has dedicated his life to God) what evil we have chosen to do that focuses the mind on just how bad sin is. And then, to have that weight lifted off us while we are most conscious of its existence is… an experience.
That is good. Even if we have already made a perfect act of contrition, we experience what exactly it is that God has forgiven us more strongly, which (at least in my experience) both strengthens the resolve to not sin again and helps us to appreciate God’s love for us.
There are also two other reasons: 1) imperfect contrition is much easier to achieve than perfect, and we don’t want to fall into the trap of lying to ourselves by pretending that we’ve achieved it when we haven’t. Again, for me at least, that first part of confession is painful enough that I have to fight past all kinds of lies I tell myself to make myself go there - despite the fact that I know that it will ultimately be a freeing and wonderful experience.
And 2) perfect contrition contains the desire to please God as best we can. Even though we know God has forgiven us, we also know that God prefers that forgiveness to be delivered through the sacrament of confession and so that we should do it.
