Satan is a liar and the father of lies. But when he goes before the throne of God to accuse us of our sin, he doesn’t have to lie, and can’t, not before God. So, for once, and only here, he tells the truth, and this to his frustration. The saints in heaven, you have to understand, were all sinners, who have been forgiven. Satan accuses them of what they did, and the saints say “Yes, that’s right! How good and kind Jesus is to have forgiven us! Praised be Jesus Christ, Son of the Immaculate Conception! Praised be God, the Father of Mercies and of all consolation! Praised be the Prince of the Most Profound Peace…” And so on. Meanwhile, Satan, confused, scampers off, defeated yet again. He. Can’t. Win. And all of this reality is really wonderful to watch. Anything less than the truth is just so boring.
BTW: This isn’t about this or that sin, or even that other one, whatever it is, whether great or small or whatever. This is especially about original sin in whose consequences we have all partaken, whether the babe just conceived or the great saints of any age.