OUTLINE:

Heb 1:3a [ad hoc expansion]
He is the radiance [light flashing forth (from)] of the glory of God and the exact imprint [an exact impression (likeness) which also reflects inner character] of his nature [God’s essence], and he upholds the universe by the word of his power.

JN 15:13
Greater love has no one than this, that someone lay down his life for his friends.

Meeter on Heb 1:3 
– from Heavenly High Priesthood
“The purification of the people was similarly achieved by blood in an act of expiation [satisfaction of God’s justice] (cf. Lev 16:30). Purity is the essential condition for participation in the cultic life. The defilement of sin erects a barrier to the approach to God which must be removed.”