A short lived inferiority - a jigsaw with 3 odd pieces

The author of Hebrews underscores the excellence of our Saviour by highlighting the key importance of our Saviour in a strange text, Psalm 8. How is this proper to apparently inject His person into this majestic description of God's goodness to man's tiny insignificance? What clues are there in the text, that this is the Holy Spirit's exact and original intention? What are the 3 missing pieces in the jigsaw?