Hebrews 1.3 says: [Jesus] is the reflection of God's glory and the exact imprint of God's very being. This is a critical piece of Christian theology that is endorsed elsewhere in the New Testament as well, especially in John's gospel: Jesus is the ultimate reflection of the nature and character of God; he tells us who God is.
Of course, the author of Hebrews also said that Long ago God spoke to our ancestors (1.1), so it would be a heinous mistake to suppose that the revelation of God in Jesus can somehow justify our negating Hebrew revelation. (My friend Derek Rishmawy discussed this issue recently on a new podcast he's got going on called "Casting Across the Pond." Listen to the insight (and awesome accents) here.)
At the same time, the revelation of God does shape our understanding of Hebrew revelation to some extent. The author of Hebrews specifically comes to an understanding that the texts of the Old Testament, especially the Psalms, especially refer to Jesus. Thus he quotes numerous psalms in the first chapter of Hebrews as interprets them as direct speech of God to the Son (vv. 5ff.). These texts somehow have a life and a meaning that transcends the specific sociohistorical context in which they had arisen, and they find their fulfillment and referent in the events surrounding Jesus.
Now I want to emphasize a particular aspect of God's glory as revealed by Jesus. The author of Hebrews, immediately upon describing the revelatory character of Jesus, affirms that he had made purification for sins (v. 3). This is especially important, to my mind: the glory of God and the representation of the very being of God is expressed in Jesus who made purification for our sins.
The same point is made other places as well. 1 John 4.8-10 makes the affirmation that God is love, that the very essence and nature of the divinity is love, and bases this judgment in the Father's sending the Son for the life and salvation of dead sinners.
It seems to me that this act -- the Creator dying at the hands of the creature for the creature's sake (cf. Rom 5.6-8) -- ought to determine our entire understanding of every other piece of theology. Judgment, sanctification, justification, hell and heaven, and the rest must all be interpreted through the lens of Christ's (God's) death for us and for our sins on the cross.
Justice is not somehow a base or determining attribute of God. If anything the divine justice is undone and cleverly deconstructed through the incarnation of God among the unjust, in order that the single just person ever to live might die for sinners. Neither is holiness the defining characteristic of God. God in Jesus Christ made regular association with the defiling presence of the unholy -- sinners, tax collectors, the diseased, and so on. There can only be one explanation of God's life for us in Jesus, and there can only be one driving factor in all of God's actions towards the world -- the one thing that remains forever (cf. 1 Cor 13.13), the love of God.