The word for "very imprint" in Greek is charakter, which refers to the impression that a stamp or seal makes on a soft surface. In the ancient world coins were made by stamping hot metal with a die on which a portrait had been engraved; the coin would bear the exact impression (charakter) of the die. The Son, then, is the exact representation of the Father. To see Jesus is to see exactly what God is like (see John 14:9; Col 1:15). In the fullest sense of the term, Jesus has the "character" of his Father.
Mary Healy, Hebrews (Catholic Commentary on Sacred Scripture)
Monday, April 3, 2017
Well Said: Jesus is the "very imprint" of the Father
Healy here comments upon Hebrews 1:3 which tells us that "Christ is "the very imprint of [God's] being."