It is a constant struggle. We start to grasp God's forgiveness and we do quite a bit better. Then we have a slip. What do we do? We go back to rationalizing. It was not that bad. Then we go back to guilt. I have blown it. I was going good but now I messed it up so God will stop blessing me. We forget that God's mercy is not just to get us started and then we can carry on using our own strength. We need His mercy every step of the way because we keep sinning. The good news is His mercy never runs out. We need to keep begging for it. We need to be constantly aware that we need it and constantly aware that it is infinite both in how long it lasts and how deep it goes. God cannot love us more. God will not love us less.
Grasping this is so important. People talk about how many personal problems are related to self esteem. Proper self esteem that is based on God's love and mercy enables us to love. It enables us to experience deep peace and joy regardless of circumstances. That, in turn, transforms all our relationships. We love God with all our heart, soul, mind and strength because we know God gives us everything and we deserve nothing. Then we love our neighbor as ourselves to.
We often know it is offered yet we can't seem to fully internalize it. That is why the divine mercy feast is so close to Easter. The key to internalizing it is grasping the mystery of the crucifixion and resurrection. The Eucharist helps us do that but we need to get what the Eucharist is. If we don't see it as a sacrifice then it does not help as much to connect us with the seriousness of our own sin and the intensity God's great mercy. Other things help to, the rosary, contemplating a crucifix, etc.
Once we grasp God's mercy towards us it helps us a lot in grasping God's mercy towards others. They become fellow sinners. They will sin differently but we need to let go of the idea that they sin worse. They are in the exact same boat as we are. The only important difference is whether they have an accurate picture of their situation and whether we do. Their problem is the same as ours. That is they are not aware of Divine Mercy. That is they are not fully embracing it. When we see other this way we just want to offer them our own mercy.