As much as we may dislike the doctrine of original sin and its consequences - it must be explored if we are ever to come to an understanding of the grace of God.
Mercy says that we are not given what we deserve. So, if that is the case, then we can all agree that we all actually don't deserve justification for our sins, we deserve hell - every last one of us. Nuns deserve hell. Pedophiles deserve hell. Preachers deserve hell. Murderers deserve hell. Politicians deserve hell. I deserve Hell. You deserve hell.
If we can't come to terms with this fact, then we will never fully understand mercy & grace. If we struggle with how a loving God could elect and save some people and not elect and save others, then we are missing point. No one deserves to be elected and saved. Should God decide, based on His pleasure, to save one soul - that is grace; He is going beyond what is required. Should he decide not to save anyone - that is justice.