What does John 6:46 mean?

The purpose of Jesus' earthly ministry was to become the link between God and men (1 Timothy 2:5). The written Word of God provides a certain level of knowledge about Him (John 5:39), but the ultimate experience of God only comes through Christ Himself (John 5:40; John 6:29). The general theme of this passage has been drawing lines between earthly, material things and heavenly, eternal things. Jesus' miraculous feeding of thousands (John 6:9–14), like Moses' provision of manna (Exodus 16), was only a sign meant to point towards a greater truth. In this case, it is that God sends the Bread of Life, in the form of a person. Those who accept this Messiah, by believing in Him, are guaranteed eternal life.

Here Jesus also repeats an important aspect of His ministry. Jesus has already claimed to have come from heaven (John 6:38). He will often claim the title of Son of Man, echoing Daniel's Old Testament prophecy (Daniel 7:13–14). As such, Jesus has knowledge which only He can possess—there are things He alone can speak of, since only He has seen them. No other human being has experienced those heavenly things. This, among other reasons, is why Jesus alone is the sole legitimate authority for spiritual truth.