Judas and Peter both sinned against the Lord. Judas actively handed over the Lord to be killed. Peter denied ever knowing the Lord who was handed over. Judas sinned against the Lord for 30 pieces of silver. Peter denied knowing Jesus in order to save his own life, to spare himself from a death like His. Yet, both Judas and Peter sinned against Jesus to better their own lives. They sinned out of selfish gain—Judas for a few more dollars in his pocket; Peter, for a few more days to his life.
They both sinned against the Lord. And they were both filled with sorrow for what they had done. But there is a difference between the outcome—Judas was lost, and Peter was saved. Why? The reason is this: "For godly grief produces a repentance that leads to salvation and brings no regret, but worldly grief produces death" (2 Corinthians 7:10). Simply put, this is the difference between Judas and Peter: Judas only had a worldly grief; Peter had a godly grief.
Judas fell into despair. He believed there would be no help or consolation for him. So, what did he do? He went out and hanged himself. He was sad; but being sad, feeling guilty, and regretting your actions is not true repentance...yet. Moping around and feeling bad for yourself is not repentance. True repentance does not only acknowledge sin against God, but it also grabs ahold of the forgiveness He gives. Judas felt sorrow over his sin, but he didn't trust that Christ would forgive him.
Peter wept bitterly when the Lord looked at him. He acknowledged his sin, grieved for it, had no love for his own sin, had no desire to continue it, and trusted that the Lord would forgive it. We know this because Peter did not end his own life. He did not despair.
Why did Judas fall into despair and not Peter? Well, Judas had been slothful in hearing the Word of God. He had been planning this sin for quite some time. With this sin consuming his mind and attention, he was slothful in hearing the Words of Christ. He despised the exhortation and consolation of His Gospel. And then, when the time came that he needed that consolation, when the time came he no longer had that Word being preached, he could not find it or hear it again. He could not find any help. He could not cling to the Lord's forgiveness and believe it in the moment of great sorrow because he did not treasure it in his heart.
Peter did not despair because he had listened diligently to the Word of Christ. He engraved that Word into his heart and mind. So, when the hour of need came, he seized it, held onto it, and comforted himself with the truth that the Lord will not count his iniquities against him. He trusted that God would be gracious to him, no matter how filthy and wicked his own heart was. Peter clung to the Word and treasured it in his heart—Judas did not.
Peter held that Word of grace close in his heart, and remembered when Jesus said, "I have prayed for you, that your own faith may not fail" (Luke 22:32).
So, learn the difference between true and false repentance. To weep bitterly over your sins is only the beginning of true repentance. Your self-pity and despondency is not true repentance. True repentance entails faith in the forgiveness God gives. Cast away the despair and doubt and unbelief that the devil tempts you with, and that Judas himself fell into. And, instead, repent truly of your sins like Peter. Know that Jesus has suffered, died, and made satisfaction for all sins. He has been punished in our place, and He forgives us all of our sins. Put your trust in Him.