When I was in 8th grade, my religion teacher explained God’s grace like a string: something that could be frayed, or even snapped entirely. The metaphor has stuck with me since then, so I’ve translated it into a series of pictures to help explain how sin and grace work.
Here we have your restless heart and God’s infinite heart. (image not to scale) This is before Baptism, because Original Sin separates you from God until Baptism unites you.
During Baptism, grace (the string) comes from God and connects His heart to yours. You have a direct line to God and nothing can hinder you from receiving that grace.
But, since we’re all human, eventually you’ll sin. If it’s just a venial sin, the grace of God is not cut off, but the strings are strained a little and your heart suffers minor tears, while God’s heart is also pained because of your sin. Receiving the Eucharist with a repentant heart and a resolution to do better can strengthen that string and heal the tears with no problem.
Mortal sin, on the other hand, completely cuts off the flow of grace. If you die in a state of mortal sin, only God knows whether the strings can be repaired. As long as you remain in this state, His heart is pained by the separation, but yours is destroyed. He’ll keep the string in case you come back, but you can’t reach it on your own.
That’s why you need the sacrament of Penance. Through the priest, God bandages you and stitches your heart back to His. It will hurt, but you are restored to a state of grace.
Eventually, you’ll die. If you die in a state of grace (free from mortal sin) you’ll go on to Purgatory. There, the scar tissue left from all the tears will be healed and your heart will be purified to prepare for the final destination.
In Heaven, there’s no need for strings that can fray and break. Your heart is united to God to be with Him for eternity.
So, what does your heart look like?