Perhaps it was the incident with the "wasted" perfume that acted as the last straw or maybe it was the many times Jesus side-stepped the opportunity to declare himself as king of Israel. We have no insight into Judas' motivation except knowing that he was a person similar to ourselves:
Then one of the Twelve—the one called Judas Iscariot—went to the chief priests and asked, “What are you willing to give me if I deliver him over to you?” So they counted out for him thirty pieces of silver. From then on Judas watched for an opportunity to hand him over. (Matthew 26:14-16)
What causes a person to betray Jesus? Learning from my own experience I would say not knowing him as we should. With all the time Judas spent with Jesus. all the miracles he saw, all the teaching he received, all the power he was involved with, Judas still did not understand. Remember that Judas was part of it all, including the rejoicing when they all came back after Jesus had sent them out, when the demons fled from them and they healed the sick and dying. Judas was not one who stood in the back, watching and not participating. He participated in everything; the feeding of the five thousand, the walking on the water, the calming of the storm, the raising of Lazarus, the ministry to the multitude, yet he did not really get it.
We can find ourselves in this same place, participating without really understanding. We can go with the crowd, expecting that God is our little good luck charm or our private little genie. Oh I know, that is not how we think we perceive it but yet what do we do when God doesn't do what we want him to do? Many of us take the matter into our own hands and try to find our own solutions. We still continue to worship and attend Bible Study but we have set Jesus aside because he wasn't doing what we wanted him to do. We do not think or act according to the Word and we never did get this whole Holy Spirit thing. We just did not get the idea of faith in Jesus, the trust thing. We trust only in what we can do for ourself.
Judas had no idea what he did at that moment of betrayal. What he expected it would lead to no one knows. Some have speculated that he was trying to force Jesus' hand, trying to make him declare himself king. However, the disciples who were there and who knew Judas said it was all about the money. Whatever his motivation, it is clear that later he understood the results of the betrayal but even then he did not understand what he could do about it. Instead of seeking forgiveness from Jesus he tried to find forgiveness by his own actions:
When Judas, who had betrayed him, saw that Jesus was condemned, he was seized with remorse and returned the thirty pieces of silver to the chief priests and the elders. “I have sinned,” he said, “for I have betrayed innocent blood.”
“What is that to us?” they replied. “That’s your responsibility.”
So Judas threw the money into the temple and left. Then he went away and hanged himself. (Matthew 27:3-5)
Judas tried to find salvation from his feelings of guilt by trying to undo what he had done. At this point it would be like trying to put the tooth paste back in the tube. What he had done could not be undone by any means, having played into the enemy's hands. However, forgiveness was still possible. All he had to do was turn to Jesus and he would have been restored just like Peter had been restored. But Judas did not understand forgiveness. He did not understand Jesus' heart. He did not understand the Father's heart. Maybe, if he had stuck around, he would have understood after the resurrection, just like Peter, but Judas could see no solution. He was so far removed from God, so lost in himself, so absorbed by self-pity and guilt that the only solution he could see was to end it all.
This is the danger of only going part way with Jesus. We can't just look at what Jesus did, we have to know the heart behind the actions. Why did Jesus cast out demons and preach the good news? What motivated him to heal the sick and give sight to the blind? What provoked him to give so selflessly of himself? What caused him to go to the cross when it was so easy for him to avoid it? What did he do that deserved death? He was innocent but in understanding his heart you will begin to understand our hope. It is not because Jesus heals us and provides for us that we follow him. It is not in the hope that he will make this miserable life a little better that we follow him. It is not the desire for reputation and reward that we follow him. We follow him because he forgave us. We follow him because he took our guilt and shame away. We follow him because he died on the cross to pay the price for our sin. We love and follow him because he loved us first. As the chorus says, "I need no other argument, I need no other plea. It is enough that Jesus died and that he died for me".
If your faith is continuing to rise and fall according to the circumstances of your life, you have yet to come to know Jesus' heart. We all have some "Judas" in us so we must move past the self to discover the selflessness of God's love. When we stop trying to find our own solutions and we start trusting in the unfailing love of our Father then the tide of our faith will stop and we will discover consistency in faith. It is important to realize and act upon the truth that Jesus saves us from all our failings because he loves us enough to forgive. We are not permitted to hold on to remorse, guilt and shame because Jesus takes all that ugliness away in the same fashion as he took it away from Peter. I know he would have taken it away from Judas if only Judas had trusted Jesus. Don't make the same mistake, don't try to find your own solutions, trust in the unfailing love of Jesus.