What does John 5:27 mean?

The title Son of Man carries great weight in the Jewish worldview. Daniel 7:13–14 presents a vision of a Promised One, in the form of a man, but with all the power and authority of God. This figure is referred to as "one like a son of man," and this phrase was commonly used as a reference to the Messiah. When used in this kind of context, the phrase "Son of Man" is not just a claim to power, but to prophecy and divinity. John uses the phrase a dozen times in this Gospel, and it's seen some eighty times in four Gospels combined.

In prior verses, Jesus has been making exactly those sorts of statements. He has claimed to possess the attributes of God (John 5:19–23), and the power over life and death (John 5:26). This fulfillment of prophecy is one reason Jesus scolds the Pharisees for ignoring the Word of God. According to Jesus, the evidence these men need to acknowledge Him is in the Scriptures already (John 5:39). And yet, those who will not accept Jesus will not accept God. Those who reject Christ are rejecting the Father (John 3:18, 36).