John Calvin Commentary Romans 15:12

"And again, Isaiah saith, There shall be the root of Jesse, And he that ariseth to rule over the Gentiles; On him shall the Gentiles hope." — Romans 15:12 (ASV)

And again, Isaiah, etc. This prophecy is the most illustrious of them all. For in that passage, the Prophet, when things were almost past hope, comforted the small remnant of the faithful by this: that a shoot would arise from the dry and dying trunk of David’s family, and a branch would flourish from his despised root, which would restore to God’s people their pristine glory.

It is clear from the account given there that this shoot was Christ, the Redeemer of the world. Then, he added that Christ would be raised as a sign to the Gentiles, so that it might be for their salvation.

The words do indeed differ a little from the Hebrew text; for we read here, arise, while in Hebrew it is stand for a sign, which is the same; for He was to appear conspicuous like a sign. What is here hope, is in Hebrew seek; but according to the most common usage of Scripture, to seek God is nothing else than to hope in Him.

But the calling of the Gentiles is confirmed twice in this prophecy: by the expression that Christ was to be raised up as a sign (for He reigns among the faithful alone), and by the declaration that they shall hope in Christ, which cannot take place without the preaching of the word and the illumination of the Spirit. The song of Simeon corresponds with these things. It may be further added that hope in Christ is an evidence of His divinity.