All the kings of the earth shall give you thanks, O Lord,
for they have heard the words of your mouth,
and they shall sing of the ways of the Lord,
for great is the glory of the Lord.
For though the Lord is high, he regards the lowly,
but the haughty he knows from afar.
So Calvin comments on the first line:
Here he declares that the goodness he had experienced would be extensively known, and the report of it spread over all the world. In saying that even kings had heard the words of God’s mouth, he does not mean to aver that they had been taught in the true religion so as to be prepared for becoming members of the Church, but only that it would be well known everywhere that the reason of his having been preserved in such a wonderful manner was God’s having anointed him king by his commandment. Thus although the neighboring kings reaped no advantage by that divine oracle, the goodness of God was illustrated by its being universally known, by his being called to the throne in an extraordinary manner. Having uniformly during the whole period of Saul’s severe and bloody persecution declared that he raised his standard in God’s name, there could be no doubt that he came to the crown by divine will and commandment. And this was a proof of divine goodness which might draw forth an acknowledgment even from heathen kings.
The stuff about King Saul is completely beside the point. Calvin is just wrong here. David’s point is precisely that Gentile kings “had been taught in the true religion so as to be prepared for becoming members of the Church.” And we will see King Hiram of Tyre at the glorious resurrection, and many others converted by Israel during the time of David and Solomon.
They are our brothers in Christ the High King.