John Calvin Commentary Psalms 89:35

"Once have I sworn by my holiness: I will not lie unto David:" — Psalms 89:35 (ASV)

Once have I sworn by my holiness. God now confirms by an oath what he previously stated he had promised to David; from this, it appears that it was not a matter of small importance, since it is certain that God would not use his holy name for something of no consequence.

It is a sign of his singular loving-kindness that, seeing our proneness to distrust, he so compassionately provides a remedy for it. We have, therefore, so much less excuse if we do not embrace his promise, which is so strongly ratified, with true and unwavering faith, since in his deep concern for our salvation, he does not withhold his oath, so that we may give full credence to his word.

If we do not consider his simple promise sufficient, he adds his oath, so to speak, as a pledge. The adverb once, denotes that the oath is irrevocable, and that therefore we have not the slightest reason to be apprehensive of any inconstancy. He affirms that he swore by his holiness, because no one greater than himself is to be found by whom he could swear.

In swearing by Him, we acknowledge him as our judge and place him as sovereign over us, just as he is our sovereign by nature.

For him to say, by my holiness, is more emphatic than if he had said, by myself. This is not only because it magnifies and exalts his glory, but also because it is far more suited to confirm faith, calling back, as it does, the faithful to the earthly dwelling place he had chosen for himself, so that they might not think it necessary to seek him from 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 unrefined understandings, swears by his holiness which dwells visibly on earth.

Regarding the elliptical form of the oath, we have seen in a previous psalm that this was a way of swearing quite common among the Hebrews. Thus they were warned that the name of God was not to be used without careful thought, lest by using it rashly and irreverently, they should bring God's vengeance upon themselves. The abrupt and suspended form of expression was, so to speak, a bridle to restrain them and give them an opportunity for reflection. It is not uncommon for God to borrow something from the common customs of people.