The Chief Priests and teachers of the law of Jesus' day thought they had a pretty good thing going: they represented their people, the Jews, before their Roman rulers, which brought with it many privileges and status. They also were the religious authorities over the Synagogue, having authority to carry out punishments - though not capital punishment - upon their people for violating any of several hundred religious traditions which they had established over the centuries.
Many of these Chief Priests and teachers were corrupt. In fact, after Aaron - the first Chief Priest (Ex. 28:3), Israel began to drift farther and farther from obedience to God and eventually lost their nation entirely to foreign rule.
Jesus, who preached a form of liberation from the legalistic system these priests had established, was a direct threat to their authority, and at the time, they also believed that Jesus sought a political overthrow of Roman rule as well. So in a kind of twisted logic, these Chief Priests and teachers, who were supposed to know the Messiah when He would come to liberate them, rationalized that it was necessary to kill Jesus the Messiah (Mark 14:1).
What an amazing example of protectionism, bias, and of ego was required! They had so lost focus of what the law meant, of the Messiah they were supposed to be waiting for, and of all objectivity that they believed they had to kill Jesus in order to preserve their own comfortable way of life.
How easily we can become just like these Chief Priests, in our hearts and in our actions. We say that we would never betray our Lord, and in the next sentence, we contradict ourselves - then defend it!
All of us have lapses in judgment - we all have biases. Our egos prevent us from seeing what is plainly bias, corruption, or rationalization, though it may be clear to others. We must face the facts: our egos are in direct conflict with God's perfect law. Were it not for Christ's great sacrifice, we would be lost. But by His grace, by the power of His Holy Spirit dwelling in us, He reveals our sins to us. When we set aside our ego and confess, He forgives us.
Absent God's grace, we would all be Christ killers. But praise be to God! He who was crucified has risen, and now helps us to see, confess, and be liberated from guilt!