Serve me - Will be my disciple, or will be a Christian. Perhaps this was said to inform the Greeks John 12:20 of the nature of his religion.
Let him follow me - Let him imitate me; do what I do, bear what I bear, and love what I love. He is discoursing here particularly of his own sufferings and death, and this passage has reference, therefore, to calamity and persecution. “You see me triumph - you see (me enter Jerusalem, and you supposed that my kingdom was to be set up without opposition or calamity; but it is not. I am to die; and if you will serve me, you must follow me even in these scenes of calamity; be willing to endure trial and to bear shame, looking for future reward.”
Where I am - See John 14:3; John 17:24. That is, he shall be in heaven, where the Son of God then was in his divine nature, and where he would be as the glorified Messiah. See the notes at John 3:13. The natural and obvious meaning of the expression “I am” implies that he was then in heaven. The design of this verse is to comfort them in the midst of persecution and trial. They were to follow him to any calamity; but, as he was to be glorified as the result of his sufferings, so they also were to look for their reward in the kingdom of heaven, Revelation 3:21; “To him that overcometh will I grant to sit with me in my throne.”