Psalms 89:37

As the moon, and as a faithful witness in heaven - That is, as long as the sun and moon shall endure, as long as time shall last, his kingdom shall last among men. The moon appears to be termed a faithful witness here, because by her particularly time is measured. Her decrease and increase are especially observed by every nation, and by these time is generally estimated, especially among the eastern nations. So many moons is a man old; so many moons since such an event happened; and even their years are reckoned by lunations. This is the case with the Mohammedans to the present day. Or the rainbow may be intended; that sign which God has established in the cloud; that faithful witness of his that the earth shall no more be destroyed by water. As long therefore as the sun, the moon, and the rainbow appear in the heavens, so long shall the spiritual David reign, and his seed prosper and increase.

Selah - It is confirmed; it shall not fail.

It shall be established forever as the moon - As long as the moon shall endure. The heavenly bodies are the most permanent objects that we know of; and they, therefore, became the emblems of stability and perpetuity. Compare the notes at Psalm 72:7.

And as a faithful witness in heaven - As the witness in heaven, or in the sky, is sure. The reference is to the moon, regarded as a witness for God. What is said here of the moon as an index of his faithfulness, might be said also of the sun and the stars; but the beauty of the image is increased by the attention being fixed to a single object. As the moon is fixed, regular, enduring - so are the promises and purposes of God. Such were the promises made to David; such was the oath which had been taken by God; such the covenant which he had made. The psalmist now proceeds Psalm 89:38-45 to show that this oath and these promises seemed to be disregarded; that there were things occurring which appeared as if God had forgotten them; that there was not that manifest prosperity and favor which was implied in the promise; but that a series of calamities had occurred which it was difficult to reconcile with these solemn pledges. On the ground of this he prays Psalm 89:46-52 that God would return, and would remember his covenant, and would bless David and his people.

89:37 A witness - The rainbow, which is God's faithful witness, a token of God's everlasting covenant between God and every living creature for perpetual generations, Genesis 9:12 ,16.