Charles H. Spurgeon on Psalms 89:35

Once have I sworn by my holiness that I will not lie unto David. Because he could swear by no greater he swore by himself, and by that peculiar attribute which is his highest glory, being the subject of threefold adoration by all the hosts of heaven. God here pledges the crown of his kingdom, the excellent beauty of his person, the essence of his nature. He does as good as say that if he ceases to be true to his covenant he will have forfeited his holy character. What more can he say? In what stronger language can he express his unalterable adherence to the truth of his promise? An oath is the end of all strife; it ought to be the end of all doubt on our part. We cannot imagine that God could lie, yet he puts it so —that if the covenant were not kept by him, he would regard it as a lie. Here is ground for strong confidence; may our faith be of such a nature as these assurances will warrant.