Verse 37. It shall be established for ever as the moon. The kingdom may wax and wane to mortal eyes, but it shall still abide as long as the moon walks in her silver beauty.
And as a faithful witness in heavens. The most stable part of the universe is selected as a type of Messiah's kingdom, and both sun and moon are made to be symbols of its long endurance. Whatever else there is in the sky which faithfully witnesses to the unbending course of nature is also called upon to be a sign of the Lord's truth. When heaven and earth witness, and the Lord himself swears, there remains no excuse for doubting, and faith joyfully reposes in confident expectation.
EXPLANATORY NOTES AND QUAINT SAYINGS
Verse 37. It shall be established for ever as the moon. This clause Kimchi expounds not only of the perpetuity, but of the quality and condition of David's Kingdom, after this fashion: If his children be good, they shall be like the moon, when full and shining; if bad, like the moon waning and obscure. Nevertheless the kingdom itself shall not cease, just as the moon does not go out of existence, whilst it is obscure, but lasts perpetually. -- Musculus.
Verse 37. And as a faithful witness in heaven. (New Translation) And as the rainbow's faithful sign. The rainbow is not expressly mentioned in the original, which speaks only of "the faithful witness in heaven." Some commentators understand the "witness" thus mentioned to be no other than the moon itself. I prefer, however, the interpretation that fixes it on the rainbow, which God after the deluge appointed as a "sign" or "witness" of his mercy in Christ. Genesis 9:12-17 . Conformably to this appointment, the Jews, when they behold the rainbow, are said to bless God, who remembers his covenant and is faithful to his promise. And the tradition of this its designation to proclaim comfort to mankind was strong among the heathens: for, according to the mythology of the Greeks, the "rainbow" was the daughter of "wonder", "a sign to mortal men", and regarded, upon its appearance, as a messenger of the celestial deities. Thus Homer with remarkable conformity to the Scripture account speaks of the "rainbow", which "Jove hath set in the cloud, a sign to men." --Richard Mant.