“the world will not see me” = McGarvey notes that “The next day the world crucified him and sealed him in the tomb, and since then has seen him no more.”

“you will see me” = the disciples were going to “see” Jesus in 2 ways: physically when He appeared to them on several occasions before His ascension, and spiritually, which applies to us even today.

The Christian life is to be one of us continually seeing an ever-present Christ. His part of that is to come and our part is to be conscious of His coming. Maclaren says that “Faith is the sight of the soul, and it is far better than the sight of the senses.” The reason he can say this is that our physical eyes only look at what they see, but faith not only gazes at what it is viewing, but also reaches out and touches it. Faith actually comes into contact with what it is perceiving. Our eyes may see something many miles away, but faith brings those things that are far away close to us.

Another reason faith is a better perceiver than our eyes or our other senses is that we may be deceived by our senses, but when our faith is built upon God’s Word, it cannot be deceived. The information it receives is always truth.

Because of this, our “seeing” Jesus, or being aware of His ever-abiding presence with us, is far better than the physical sight His disciples had of Him while He was in the flesh. Our vision of Him is loftier, better and greater than that of those who saw Him while He was on this planet. Jesus stated this concept in (John 20:29). We all desire a physical manifestation of Christ. We are like Thomas who wanted to touch the nail holes before he would believe. We demand a physical manifestation of His provision, and we want it immediately. How will we ever grow spiritually if we keep our eyes fixed on this world instead of upon Him? Maclaren said it well when he stated that “If you want the eye of the soul to be opened, you must shut the eye of sense.” We need to follow the directions given us in (Col 3:1-4).

John 20:29  Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.”

Colossians 3:1-4  Since, then, you have been raised with Christ, set your hearts on things above, where Christ is seated at the right hand of God.
  Set your minds on things above, not on earthly things.  For you died, and your life is now hidden with Christ in God.  When Christ, who is your life, appears, then you also will appear with him in glory.

“Before long” indicates again that Jesus is speaking of His post-resurrection appearances.

“Because I live, you also will live.” = This was not a new thing He was revealing to them (John 6:57), but it is certainly a good thing, and one that needs repeating. The resurrection of Jesus was going to be the guarantee that death would have no hold over them, either. His living is the pledge that we will live. This means that as long as Christ lives, so will we, and since He is God, He will live eternally. What a promise! Note also (Rev 1:18).

John 6:57  Just as the living Father sent me and I live because of the Father, so the one who feeds on me will live because of me.

Revelation 1:18  I am the Living One; I was dead, and behold I am alive for ever and ever! And I hold the keys of death and Hades.