Heb. 2:6-8

Heb 2:6 But one in a certain place testified, saying, What is man, that thou art mindful of him? or the son of man, that thou visitest him?

Heb 2:7 Thou madest him a little lower than the angels; thou crownedst him with glory and honour, and didst set him over the works of thy hands:

Heb 2:8 Thou hast put all things in subjection under his feet. For in that he put all in subjection under him, he left nothing [that is] not put under him. But now we see not yet all things put under him.

Why does the author cite Psalm 8:4-6?

Ps 8:4 What is man, that thou art mindful of him? and the son of man, that thou visitest him?

Ps 8:5 For thou hast made him a little lower than the angels, and hast crowned him with glory and honour.

Ps 8:6 Thou madest him to have dominion over the works of thy hands; thou hast put all [things] under his feet:

Ps 8:7 All sheep and oxen, yea, and the beasts of the field;

Ps 8:8 The fowl of the air, and the fish of the sea, [and whatsoever] passeth through the paths of the seas.