In this vein, the Hagadah states: ‘The rasha, what does he does he say? ‘What is this service to you?’ ‘To you’ and not to him. Since he removed himself from the public, he denies the main thing. You too, blunt his teeth and tell him: Because of this Hashem did it for me when I went out of Egypt. ‘For me’ and not for you. If you had been here, you would not have been redeemed.’
The Yismach Yisroel says that this is not speaking about an actual rasha. Rather, it is referring to one who has done some sins and has despaired of ever doing teshuva because he thinks that he was sunk too far to ever get out of the mud. He is called a ‘kofer b’ikur’ because he removes himself from the public by thinking that he can never do teshuva and rejoin them. We are told to blunt his teeth and say that Hashem ‘took me’ out of Egypt. In Egypt, the nation had also sunk to a low level of impurity, but Hashem still redeemed them. So too, he can redeem this person and he is obligated to believe that.
On this night, the power to lift a person up from his lowliness returns, and even one who is stuck on a very low level, can be brought back up if he just believes in Hashem and trusts Him to help him.