Someone said to Reb Yisrael Salanter zy’a “I am set in my ways; I don’t think I’ll ever do teshuvah.”

Reb Yisrael Salanter rebuked him, “Chazal tell us that when we blow the shofar on Rosh Hashanah, the Satan gets frightened because he fears that we’ve done teshuvah and what he hears is the shofar of Moshiach.

So you see, even the Satan believes that you can do teshuvah. Why don’t you believe it?” ~ R’ Elimelech Biderman Shlita