Ezra declared in Nehemiah 8:10 that “The joy of the Lord is your strength.” His joy is our strength; it is what keeps us going when we do not know if we can carry on. It lifts us up, surrounds us, and empowers us. Jesus tells God in John 17:13 that he had told the people many things so that they would have joy after He was gone.
The things that Jesus said would stay with the people long after His death. We are the evidence that those things impacted the people. In Acts 2, the Holy Spirit comes on the people and they begin to speak in tongues. They were able to understand each other because of the interceding of the Holy Spirit. They were filled with awe. Peter began to preach and the hearts of thousands were added to their number that day. What happened afterward was more evidence of the joy that lived in the hearts of the people. They began meeting in homes and sharing all things; God continued adding to their number.
That is what joy does. It saves. It grows. It witnesses. Jesus shared His joy with the people so that they would spread His joy and continue adding to the redeemed.