I think it would be best to look at a slightly longer passage: John 14:18-20. I will take the passage one phrase at a time and make comments on it.
John 14:18-20 I will not leave you comfortless: I will come to you. Yet a little while, and the world seeth me no more; but ye see me: because I live, ye shall live also. At that day ye shall know that I am in my Father, and ye in me, and I in you.
John 14:18: "I will not leave you comfortless" -- Comfort is an abiding strength. That is, a comfort is something that stays with us and gives us strength and help. The word ends with "fort." The beginning of the word, "com-," means "with." So, a comfort is a fortification (a stronghold) that stays with us wherever we go. During the earthly ministry of Jesus, He had been the comfort of His disciples. He was there to tell the disciples, "Fear not." On one occasion He said, "Fear not, little flock" (Luke 12:32). Here we see the picture of a shepherd comforting His frightened sheep.
John 14 records words that Jesus said to His disciples on the evening He was arrested. He would be crucified the next morning. He is telling them things that they had not been ready for earlier. He had just told them that He was going away, though He did not explain that it was by death. His disciples were troubled. They did not know what they would do without Jesus. They did not understand why they could not go with Him. Jesus begins this section of His words to them by assuring them that He would not leave them comfortless. He would not leave them without strength; without the help they must have.
John 14:18: "I will come to you" --Although the Comforter, the Holy Ghost, would be sent to them and He is in context (John 14:16), Jesus Himself would also return to them. For several reasons we will see below, the return He is referring to here is the one where He appeared to them after his resurrection.
John 14:19: "Yet a little while" -- Here we see that Jesus would come to them in "a little while." This cannot refer to the coming that has not yet occurred 2,000 years later. Therefore, it does not refer to the second coming of Christ. Rather, it refers to His resurrection appearances to the disciples and other believers.
John 14:19: "and the world seeth me no more; but ye see me" -- When He returns to them in a little while, the world will not see him, but His disciples will see Him. This is certainly the case with the post-resurrection appearances of Christ. There is no reason to believe that He was invisible to the world as a spirit would be. The point is that He did not reveal Himself to the world in His resurrection appearances. The most complete listing of these appearances is found in 1 Corinthians 15:5-8. Every last appearance was to believers. In one meeting, He was "seen of above five hundred brethren at once" (1 Corinthians 15:6), yet notice that they were "brethren." They were believers. Jesus had come to the world and they had rejected Him. This return was to assure His disciples of His victory over death, hell, and the grave.
John 14:19: "because I live, ye shall live also" -- By proving to them that He had risen from the dead, He gave them confidence in their own resurrection. Since He arose from the dead, He had the power to raise them from the dead. If you would carefully read the sermons recorded in the book of Acts, you would see that the theme of these sermons is the resurrection from the dead. Their hope of eternal life was based on the resurrection of Jesus Christ. They saw the resurrected Christ and His appearances gave them the confidence (the comfort) to take the gospel of Christ to all the world.
John 14:20: "At that day ye shall know that I am in my Father" -- When the disciples see the risen Saviour, they will have a knowledge, a confidence, and a faith in His connection to the Father that exceeds everything they experienced during His lifetime. They will know indeed that the Son and the Father are one. They will know that everything the Son told them was from the Father; that everything the Son did was the work of the Father. They will know that connection and have confidence in it as never before.
John 14:20: "and ye in me, and I in you" -- Finally, they will understand their relationship to the Son as never before. They will see that they are in Him and they will see that He is in them. They will see their spiritual union with the Lord Jesus Christ. The following verses expand a little on this union. The epistles of the New Testament continually come back to this theme. We who know Jesus Christ as our Saviour are in Christ; in Him. Yet, He also abides in us. Why is this so? It was sealed with the resurrection of Jesus from the dead and the disciples were comforted by this fact when they saw the resurrected Christ. We learn of the same fact from their testimony and teaching as found in the New Testament. What a glorious blessing!
I am not familiar with the teachings of the Jehovah Witnesses in great detail. I know that they teach of a coming of Jesus to his followers that is already past and evidently they use this verse to teach it. However, there are several reasons that this passage refers to the appearance of Christ after His resurrection to His disciples:
- It occurred "a little while" after He told them it would happen. This cannot refer to something that happened about 1900 years afterward.
- The disciples saw him, but the world did not. This best fits the post-resurrection appearances which were always to believers.
- This gave them confidence in their own resurrection. What could give more confidence than seeing Jesus shortly after they had seen Him die on the cross?
- This appearance gave them confidence in the relationship if Jesus to the Father and the disciples' relationship to Jesus. Jesus did not make His disciples wait 1900 years to have that assurance. He gave to them immediately after His resurrection. The New Testament authors talked of it constantly.