What is the explanation of the Hadith: "The one who repents from sin is like one who has no sin," and what is meant by the phrase "Hadith Hasan"?

The Prophetic Hadith "One who repents from sin is like one who has no sin" is established by the totality of its chains of transmission and corroborating evidence. Many scholars have deemed it hasan (good) and sahih (authentic). As for the additions found in some narrations, such as "And if Allah loves a servant, no sin will harm him," these are weak. The meaning of theith is that when a servant repents to Allah Almighty with sincere repentance from a sin, Allah forgives him and treats him as if he had never sinned. Furthermore, He replaces his bad deeds with good ones, loves him, makes him among the pious, and it becomes as if he had never committed that sin at all.