"What is man....that you visit Him?"

In Hebrews 2 the author quotes portions of Psalm 8.
To what man does Psalm 8 historically refer?

Based on Genesis 1:26-28, Psalm 8 must refer to Adam as the first man who was “crowned with glory and honor” and “given dominion.”

To whom does Psalm 8 refer prophetically?

Prophetically, Psalm 8 must refer to the last Adam when compared with Romans 5:13ff, 1 Corinthians 15:20ff and Hebrews 2:8. Bruce shows that Paul references this in Philippians 2:6-11 (Bruce 1990, 73)

Jesus affirms this in Matthew 21:16 as he applies the praise of the children in Psalm 8:2 to His welcome on “Palm Sunday.”

How does Hebrews’ author use this prophetically?

Hebrews applies this prophetically to Jesus’ exaltation already declared in 1:13 but delineated in 2:5 where he says it occurs in “the world to come.”

What does the author mean that not all things are presently subjected to Jesus?
It is the tension between 1:13 and 2:5. It occurred in 1:13, but is quite real in our perspective in 2:5: “the world to come.” This is, without a doubt, the issue eluded to in Matthew 6’s model prayer where the “will of the Father which is done in Heaven” is desired “on earth.” The now of “shadows” will soon be, in the mind of the Hebrews’ author, the “world to come” of “substance."