Romans 15:9

‘And that the Gentiles might glorify God for his mercy, as it is written, “Therefore will I give praise to you among the Gentiles, and sing to your name.” '

And He has also come in order that the Gentiles might glorify God for His mercy, something which Paul now demonstrates by citing a number of Scriptures which confirm the acceptance of the Gentiles and lead up to their also benefiting from the Root of Jesse. We have in these descriptions shades of Romans 11:16. The Root of Jesse has produced the holy branches of the true Israel, composed of both Jews and Gentiles, who will now glorify God together. It is possibly significant for our interpretation of the olive tree that the promises of the fathers are not here linked to the Gentiles (although they are of course elsewhere). It is true that God's blessing of the nations was a part of those promises, but that is not the point that is being made by Paul. The point being made is rather that the believing Gentiles glorify God and benefit from the Root of Jesse. This may be seen as confirming that the root of the olive tree in Romans 11:16 has in mind the Messiah.

We note again that the four citations cover the three sections of the Scriptures, the Torah, the Prophets and the Holy Writings. The first citation above is taken from Psalms 18:49, where David's own rulership over the Gentiles as ‘the anointed one', and that of his seed for ever (Psalms 18:50), are proclaimed, a rulership which results in him and his successors glorifying God before the Gentiles. Paul thus sees it as indicating that the Gentiles will submit themselves to the Messiah, the Anointed One and seed of David par excellence, Who will glorify God to them.