John Calvin Commentary Psalms 73:27

"For, lo, they that are far from thee shall perish: Thou hast destroyed all them that play the harlot, [departing] from thee." — Psalms 73:27 (ASV)

For, lo! they who depart from thee shall perish. Here he proves, by an argument from contrary things, that nothing was better for him than simply to repose himself upon God alone; for no sooner does anyone depart from God than he inevitably falls into the most dreadful destruction.

All depart from him who divide and scatter their hope among a variety of objects. The phrase to go a whoring is of similar meaning; for it is the worst kind of adultery to divide our heart so that it may not continue fixed exclusively upon God. This will be more easily understood by defining the spiritual chastity of our minds, which consists in faith, in calling upon God, in integrity of heart, and in obedience to the Word. Whoever then does not submit himself to the Word of God, and so does not recognize him as the sole author of all good things, nor depend upon him, surrender himself to be governed by him, turn to him at all times, nor devote all his affections to him—such a person is like an adulterous woman who leaves her own husband and prostitutes herself to strangers. David’s language then is equivalent to his pronouncing all apostates who revolt from God to be adulterers.