The Ashkenazi Chief Rabbi David Lau, gave a clear explanation of the difference between תשובה מאהבה, repentance out of love, and תשובה מיראה, repentance out of fear.
With תשובה מיראה, one’s sins are transformed to שגגות, as if he did them unintentionally, but the sins are still there. With תשובה מאהבה, the sins are transformed into merits. The sins are viewed as Mitzvot.
Rav Lau explains that one who acts out of fear, is afraid of punishment. He is not necessarily remorseful of his past transgressions. While the one who has now acquired love of Hashem acts on this love and he is very remorseful. This is the reason for such a dramatic difference in results.
May we all be זוכה to do תשובה מאהבה, and may all of our sins turn into Mitzvot.