The 11th of Jonathan Edwards' famous resolutions says:

Resolved, when I think of any theorem in divinity to be solved, immediately to do what I can towards solving it, if circumstances don't hinder.

To paraphrase: Bible understanding really matters. And good Bible handling really matters. Matters to the extent of spending time on bits I don't understand, staring at them, wrestling with them, finding out why the writers write what they do, the way they do. If I just pass over the difficult stuff it shows I don't really want God in the way God reveals himself.

I have paused off another post on Hebrews to spend some time thinking about the way the writer quotes the Old Testament in chapter 1. It is full of Old Testament quotes, and the purpose is obvious: to show that Jesus is superior to angels (and therefore superior to the Old Covenant). But what's been playing on my mind is not why he quotes the Old Testament, but how. He seems to take some texts which in their original context are manifestly not directly about Jesus and say that they are. Does this mean it is OK to rip a text out of context and make it mean something different to the original writer? Was the writer to the Hebrews a postmodernist??

You might read this and think it is simply unimportant. Who cares? Well God cared enough to make sure it got written in this way for us. He has told a whole sweep of the story of his dealings with his people and the world and Hebrews is drawing on all of that to proclaim the supremacy of Jesus, so I think its a mighty and weighty thing to try to figure out.

There are 7 quotations in chapter 1. Each one assumes that it is OK to take an Old Testament text and apply it to Jesus Christ. Why? What assumptions does the writer make about the Old Testament that make that a valid thing to do?

The first two (v5) are about the Son. These ones are quite easy to figure. In their original context they are about the relationship between Yahweh and the King of Israel. The relationship was so close that the King was called the Son of God. The writer sees a trajectory from an imperfect kingship to a perfect divine kingship and says "what the Old Testament says about God and the Son is perfectly applicable to the Ultimate Son and King - Jesus."
The pair of quotes in v7-8 are also not too difficult. He establishes the mighty power of angels, but then blows it away with a quote from a psalm about the wedding of God's King (Ps45). The psalm refers to the King as the vice-regent of Yahweh, the powerful agent of Yahweh, the messiah of Yahweh and, in some sense, the image of Yahweh. So much so that the King can be called "God". With prophetic insight the psalm looks forward, and Hebrews applies, the fact that there will be a perfect King who is God with an eternal reign. And that's Jesus
The final quote (v13) from Ps 110 works he same - promises God makes to the King of Israel are finally applied to the ultimate King.

But then there is v6 and v10-12, and they are difficult. Or I think they are, anyway. In these verses the writer doesn't apply Old Testament quotes about the King saying "that's Jesus". v6 is an Old Testament quote about God. And verses 10-12 are even stranger: in Ps 102 they are the King addressing God, here in Hebrews the writer takes them to be God addressing the Son/King.

How does it work? I am sure I have a long way to go. Two assumptions seem inescapable:

Hebrews assumes that Jesus is the perfect Son, is the perfect God/King, is the image of God, is God. And therefore stuff that the Old Testament says about God can be applied directly to Jesus just as much as stuff about the King
Everything written by an Old Testament writer like the Psalmist is also written by God. Utterances about God are therefore also utterances of God. That is, everything in the Bible is what God says about God. Therefore, having established that Jesus is God, the writer thinks it is appropriate to take a Psalm abut God's mighty act of creation (and eventual recreation) and use apply it directly to Jesus

These Old Testament applications are only valid therefore under the following assumptions:

Jesus is the final, perfect God/King about which texts about the King spoke
Jesus is Yahweh, about whom the texts about God spoke
God writes everything in the Bible and therefore the whole Bible is utterances of God as well as utterances about God
The whole plotline is pointing to what God will do finally in Jesus

Pressing through on why the writer quotes the way he does matters. It gives a weight of authority to Jesus, a trajectory to figure out Old Testament texts, and a glorious understanding of Davidic Kingship in the Old Testament that we would otherwise miss.