And they returned to Jerusalem with great joy. Luke 24:52
Who did? The disciples.
When? After they had just seen Jesus leave them and rise up into heaven.
But He was leaving them, --their closest friend He was leaving them. How could they return with great joy?
Because all the time He had been on earth with them and especially during these past 40 days after He rose from the dead. He had been teaching them and explaining to them how all the events of the Old Testament, -- all the things they couldn't understand -- were all meant to happen this way, and why. Jesus taught them the Old Testament Scriptures in a way they had never understood before.
Now that He was truly gone, they knew why. They knew why He had to die and why He rose from the dead. It all made sense to them now. Not only that, they now knew what they had to do. Jesus had left them with a promise and a task. The promise was that the Holy Spirit would come upon them and they would be given the power to do the task that He had set for them. They were to spread the good news that through Jesus we can have our sins forgiven and go to be with Him in Heaven. They knew this as a certainty. No wonder they were rejoicing!