You have heard Me say to you, “I am going away and coming back to you.” If you loved Me, you would rejoice because I said, “I am going to the Father.”
In order for Jesus to give us what He promised, it was necessary for Him to go back to heaven. He says in verse 28, “You have heard Me say to you, ‘I am going away and coming back to you.’ If you loved Me, you would rejoice because I said, ‘I am going to the Father.’ ” Jesus is reminding His disciples (and us) that before His peace could flood their hearts, it was necessary for Him to ascend back to heaven and be with the Father.
You may wonder why that was true. I believe it was because the peace of the Lord Jesus is resident in the Person of the Holy Spirit, and the Holy Spirit could not be poured out upon mankind as He was at Pentecost until Jesus Christ ascended back to the Father. Jesus had just told the disciples (vv. 25–26) that the Holy Spirit would be sent by the Father after Jesus was no longer present with them. Because the Holy Spirit is resident in the life of every believer, it becomes possible for every believer to experience peace (Galatians 5:22).
 Jeremiah, D. (2002). Sanctuary: finding moments of refuge in the presence of God (p. 116). Nashville, TN: Integrity Publishers.