John affirms this glory in John 1:14 saying, “And the Word became flesh, and dwelt among us, and we beheld His glory, glory as of the only begotten from the Father, full of grace and truth.” So Jesus goes on to say that when they receive that glory of the truth, they will be “perfected in unity, so that the world may know that You sent Me, and loved them, even as You have loved Me.” Perfected means completed. Our unity with God is completed when we know the truth of God in Jesus Christ. And when we are complete in our knowledge of the truth, then we can fulfill the mission of the church, which is to go into all the world and make disciples. When we know the truth about Christ, then we can make Him known to the world, that the world might come to a saving knowledge of God.
Jesus was going away back to the Father. He has told them this over and over again. In fact, at the beginning of the Upper Room Discourse He said, “Let not your heart be troubled: you believe in God, believe also in me. In my Father's house are many mansions: if it were not so, I would have told you. I go to prepare a place for you. And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there you may be also.” (John 14:1)