For, lo! they who depart from thee shall perish. Here he proves, by an argument taken from things contrary, that nothing was better for him than simply to repose himself upon God alone; for no sooner does any one 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 [1] is of similar import; for it is the worst kind of adultery to divide our heart 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 submits not himself to the Word of God, that feeling him to be the sole author of all good things, he may depend upon him, surrender himself to be governed by him, betake himself to him at all times, and devote to him all his affections, 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.

Footnotes

1 - "Go a whoring, etc.; i.e., forsake God for false gods, which is spiritual adultery." -- Sutcliffe. When God is said to have destroyed such as do this, some think there is an allusion to that part of the Mosaic law which doomed idolaters to be punished with death, as guilty of high treason against Jehovah the King of Israel.

For, lo, they that are far from thee shall perish - All that are estranged from thee; all who are not thy friends. They will certainly be destroyed. For them there can be no hope. This is the fact which solved the difficulty of the psalmist in regard to the divine dealings with people, Psalm 73:3-7. The fact that there will be a righteous judgment, in which God will deal with people according to their deserts, made all plain. Compare Psalm 73:16-20.
Thou hast destroyed - That is, Thou wilt certainly destroy. The psalmist places himself in the future, and speaks of this as if it were already done. It will be so certainly done that he could speak of it as if it were already accomplished.
All them that go a whoring from thee - The relation of God to his people is often compared in the Scriptures with the marriage relation (compare Ps. 45); and a departure from Him is compared with a want of fidelity to the marriage contract. See Matthew 12:39; Matthew 16:4; Jeremiah 3:8-9; Jeremiah 5:7; Jeremiah 13:27; Ezekiel 23:37; Revelation 2:22 :

They that are far from thee shall perish - The term perish is generally used to signify a coming to nothing, being annihilated; and by some it is thus applied to the finally impenitent, they shall all be annihilated. But where is this to be found in the Scriptures? In no part, properly understood. In the new heavens and the new earth none of the wicked shall be found; for therein dwells righteousness - nothing but God and righteous spirits; but at the same time the wicked shall be in their own place. And to suppose that they shall be annihilated, is as great a heresy, though scarcely so absurd, as to believe that the pains of damnation are emendatory, and that hellfire shall burn out. There is presumptive evidence from Scripture to lead us to the conclusion, that if there be not eternal punishment, glory will not be eternal; as the same terms are used to express the duration of both. No human spirit that is not united to God can be saved. Those who are Far from Thee shall perish - they shall be lost, undone, ruined, and that without remedy. Being separated from God by sin, they shall never be rejoined; the great gulf must be between them and their Maker eternally.
All them that go a whoring from thee - That is, all that worship false gods; all idolaters. This is the only meaning of the word in such a connection. I have explained this elsewhere.

For, lo, they that are far from thee shall perish: thou hast destroyed all them that (p) go a whoring from thee.
(p) That is, forsake you to seek others.

For, lo, they that are far from thee,.... Who are alienated from the life of God, far from the law of God, and subjection and obedience to it; and from righteousness either moral or evangelical, and from the love and fear of God, and worship of him:
shall perish; not merely at death, as even righteous men do, but be lost eternally:
thou hast destroyed all them that go a whoring from thee; that follow after other gods, and worship them; which is spiritual adultery and fornication, the Scriptures often speak of, and intend by it idolatry; see Deuteronomy 31:16 or who set their hearts and affections upon the creature, and have them alienated from God; and love the creature more and besides the Creator: the past tense seems to be put for the future, and so some render it, "thou shalt destroy", or "cut off" (i); destroy them soul and body, and punish them with an everlasting destruction in hell; the Targum is,
"that wander from thy fear;''
that is, from the worship of God.
(i) "perdes", Tigurine version, Musculus, so some in Vatablus; "exscindes", Michaelis.

The lot of apostates, described by a figure of frequent use (Jeremiah 3:1, Jeremiah 3:3; Ezekiel 23:35), is contrasted with his, who finds happiness in nearness to God (James 4:8), and his delightful work the declaration of His praise.

The poet here once more gives expression to the great opposites into which good fortune and misfortune are seemingly, but only seemingly, divided in a manner so contradictory to the divine justice. The central point of the confirmation that is introduced with כּי lies in Psalm 73:28. "Thy far removing ones" was to be expressed with רחק, which is distinct from רחוק. זנה has מן instead of מתּחת or מאחרי after it. Those who remove themselves far from the primary fountain of life fall a prey to ruin; those who faithlessly abandon God, and choose the world with its idols rather than His love, fall a prey to destruction. Not so the poet; the nearness of God, i.e., a state of union with God, is good to him, i.e., (cf. Psalm 119:71.) he regards as his good fortune. קרבה is nom. act. after the form יקהה, Arab. waqhat, obedience, and נצּרה, a watch, Psalm 141:3, and of essentially the same signification with ḳurba (קרבה), the Arabic designation of the unio mystica; cf. James 4:8, ἐγγίσατε τῷ Θεῷ καὶ ἐγγιεῖ ὑμῖν. Just as קרבת אלהים stands in antithesis to רחקיך, so לי טּוב stands in antithesis to יאבדו and הצמתה. To the former their alienation from God brings destruction; he finds in fellowship with God that which is good to him for the present time and for the future. Putting his confidence (מחסּי, not מחסי) in Him, he will declare, and will one day be able to declare, all His מלאכות, i.e., the manifestations or achievements of His righteous, gracious, and wise government. The language of assertion is quickly changed into that of address. The Psalm closes with an upward look of grateful adoration to God beforehand, who leads His own people, ofttimes wondrously indeed, but always happily, viz., through suffering to glory.

Go a whoring - Those who revolt from thee, to work wickedness; which is called whoredom in scripture.