"Do what you came for, friend." (Matthew 26:50)

While he was still speaking, Judas, one of the Twelve, arrived. With him was a large crowd armed with swords and clubs, sent from the chief priests and the elders of the people. Now the betrayer had arranged a signal with them: "The one I kiss is the man; arrest him." Going at once to Jesus, Judas said, "Greetings, Rabbi!" and kissed him. Jesus replied, "Do what you came for, friend." Then the men stepped forward, seized Jesus and arrested him. (Matthew 26:47-50)

Why was Jesus so kind to his arresters?

How many people do we know that would greet a large crowd of armed thugs who came to arrest them with such kind words? Few if any.

This statement by Jesus says three things. First, it confirms other statements by Jesus, as well as his prayers, that he knew this would please God. Why? Because Jesus was standing up for his teachings. He wasn't running away.

This is confirmed by his telling his disciples after Judas left just prior to his arrest:
"Now is the son of man glorified and God is glorified in him." (John 13:31)
Secondly, this also indicates that Jesus was not surprised by his arrest. He was not only fully aware of what would happen, but had a hand in the arrangements of his arrest. This is confirmed as Jesus spoke the following to Judas before Judas left to get the guards:
"What you are about to do, do quickly," Jesus told him, but no one at the meal understood why Jesus said this to him. (John 13:27-28)
The third thing that Jesus' statement says is that even with his arrest by adversarial guards sent by the institutional temple priests to capture him, Jesus still loved them. He called him (likely the lead guard) "friend." Is this how a person greets someone who will shackle him and arrest him?

But Jesus is not a typical person. He is the representative of God, and the loving servant of God, and in his love for God, he loved them. He cared for them. This is because he saw them not as his arresters, nor even humans. He saw them as wayward children of God - spiritual beings - who were occupying temporary physical bodies. Jesus communicated many times the distinction between the person and the physical body:
"The spirit is willing, but the body is weak." (Matthew 26:41)
"Do not be afraid of those who kill the body but cannot kill the soul." (Matthew 10:28)

Jesus knew only his body would be killed

This indicates that Jesus differentiated between the physical body and the spiritual person within the body. We are each spiritual in essence, not physical. As our body ages from the baby body to the elderly body, we remain the same person within. We do not die when the body dies. This spiritual identity is not visible with the eyes, but Jesus saw each spiritual person within each of the physical bodies of the guards.

Jesus also did not blame them. He understood that all this was taking place by God's will, as he prayed just before his arrest:
"My Father, if it is not possible for this cup to be taken away unless I drink it, may Your will be done." (Matthew 26:42)
So Jesus was willingly being arrested because he was doing what was pleasing to God. Why? Why would a person willingly be arrested, tortured and even murdered?

Because Jesus loves God. He loves the Supreme Person, and he was willing to sacrifice his physical comfort and physical body to please the One he loves. This act served to illustrate, in practical terms, Jesus' most important teaching:
'Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment." (Matt. 22:37-38)