When Jesus had spoken these words, he went out with his disciples across the brook Kidron, where there was a garden, which he and his disciples entered.
John 18:1 ESV
There was a brook called the Kidron between the room where the Last Supper was held and the place where Jesus was betrayed. Of course they had to cross it. At first this seems like an unimportant detail, but there is an incident in the Old Testament which shows the significance of going across this brook.
When David was forced to flee from Jerusalem to escape his rebellious son Absalom, he encountered a man named Shimei.
When King David came to Bahurim, there came out a man of the family of the house of Saul, whose name was Shimei, the son of Gera, and as he came he cursed continually. And he threw stones at David and at all the servants of King David, and all the people and all the mighty men were on his right hand and on his left.
And Shimei said as he cursed, “Get out, get out, you man of blood, you worthless man! The LORD has avenged on you all the blood of the house of Saul, in whose place you have reigned, and the LORD has given the kingdom into the hand of your son Absalom. See, your evil is on you, for you are a man of blood.”
2 Samuel 16:5-8 ESV
David did not punish Shimei, either then or when he was restored to his kingdom, but after Solomon became king he did punish him.
Then the king sent and summoned Shimei and said to him, “Build yourself a house in Jerusalem and dwell there, and do not go out from there to any place whatever. For on the day you go out and cross the brook Kidron, know for certain that you shall die. Your blood shall be on your own head.”
And Shimei said to the king, “What you say is good; as my lord the king has said, so will your servant do.” So Shimei lived in Jerusalem many days.
1 Kings 2:36-38 ESV
For Shimei, crossing the Kidron meant choosing to die. If you read 1 Kings 2:39-46 you will find that he did disobey Solomon and was executed.
Crossing the Kidron had the same significance for Jesus as for Shimei; he was choosing to die. The difference is that Shimei’s death was the result of his disobedience to Solomon while the death of Jesus was in obedience to God. He chose to die to atone for our sins so we could be forgiven and reconciled to God.
Judas had left the group of disciples earlier to betray Jesus to the religious leaders so they could kill him. He obviously knew where Jesus planned to go after the feast and he led a group of soldiers there so they could arrest him. Jesus could have avoided being arrested and killed simply by not crossing the Kidron but if he had done so none of us would have anything to look forward to after death except God’s judgment and punishment for our sins.