Hebrews 1:5

‘And again, “I will be to him a Father, And he will be to me a Son?” ’

Or ‘And again, “I will be to him as a Father, And he will be to me as a Son.” ’ ‘And again’ (kai palin), signifies the introduction of a further witness from Scripture. This quotation is taken from 2 Samuel 7:14. Note the use of eis (unto) in the predicate with the sense of "as" like the Hebrew (an LXX idiom), not necessarily needing to be preserved in the English. See Matthew 19:5; Luke 2:34.

The same passage is applied to the relationship between God and His people see 2 Corinthians 6:18; Revelation 21:7, but not there with Messianic implications except in so far as they are spoken to the Messianic community.

These words were spoken after David had determined to build a Temple for Yahweh and God had come back with the reply that He did not want a temple, only a tent, but that in view of David’s faithfulness He would build for David an everlasting house, a living house of successive kings so that his throne would be established for ever. And this would begin with his son.

Yahweh then promised that He would be his father and would adopt him as His son (2 Samuel 7:5-16). And this relationship, along with the right to the throne, would then go on for ever in his descendants (2 Samuel 7:16). It would therefore also apply to the final everlasting king (Ezekiel 37:25). Intrinsic within the promises is potential for the kings who follow David to have a special relationship with God as appointed by Him, with a recognition of a greater Messianic fulfilment.

Again, once the Davidic house faded this became firmly attached to the necessary idea of a future coming king (which is intrinsic in the words) which eventually resulted in the words specifically being applied Messianically (as witnessed in the Dead Sea Scrolls). Thus, says the writer, God promised to the Messiah that He would be His Father, and He would be His Son.

So in both promises we have the assurance that the Messiah would be greater than the angels for He would be God’s Son, and God would be His Father. Such a relationship is never suggested of angels, and makes clear that the Sonship is no earthly expedient.