Psalms 89:35

35. Once have I sworn by my holiness. God now confirms by an oath what he previously stated he had promised to David; from which it appears that it was not a matter of small importance; it being certain that God would not interpose his holy name in reference to what was of no consequence. It is a token of singular loving-kindness for him, upon seeing us prone to distrust, to provide a remedy for it so compassionately. We have, therefore, so much the less excuse if we do not embrace, with true and unwavering faith, his promise which is so strongly ratified, since in his deep interest about our salvation, he does not withhold his oath, that we may yield entire credence to his word. If we do not reckon his simple promise sufficient, he adds his oath, as it were, for a pledge. The adverb once, denotes that the oath is irrevocable, and that therefore we have not the least reason to be apprehensive of any inconstancy. He affirms that he sware by his holiness, because a greater than himself is not to be found, by whom he could swear. In swearing by Him, we constitute him our judge, and place him as sovereign over us, even as he is our sovereign by nature. It is a more emphatic manner of expression for him to say, by my holiness, than if he had said, by myself, not only because it magnifies and exalts his glory, but also because it is far more fitted for the confirmation of faith, calling back, as it does, the faithful to the earthly habitation which he had chosen for himself, that they might not think it necessary for them to seek him at a distance; for by the term holiness, I have no doubt, he means the sanctuary. And yet he swears by himself, and by nothing else; for, in naming the temple which he had appointed as his seat, he does not depart from himself; but, merely accommodating his language to our rude understandings, swears by his holiness which dwells visibly upon earth. With respect to the elliptical form of the oath, we have seen, in a previous psalm, that this was a manner of swearing quite common among the Hebrews. Thus they were warned that the name of God was not to be used without due consideration, lest, by using it rashly and irreverently, they should draw down upon themselves the Divine vengeance. The abrupt and suspended form of expression was, as it were, a bridle to restrain them, and give them opportunity for reflection. It is no uncommon thing for God to borrow something from the common custom of men.