Envy sinners - Compare in Psalm 37:1; Psalm 73:3; the feeling which looks half-longingly at the prosperity of evil doers. Some connect the verb "envy" with the second clause, "envy not sinners, but envy, emulate, the fear of the Lord."

Let not thine heart envy sinners,.... Their present prosperity and happiness, the pleasure, profit, and honour, they seem to enjoy; all which is but a shadow, fading had temporary; and yet good men are apt to envy it in their hearts, if they do not express it with their lips; and are ready to murmur and think it hard that they should be in straitened circumstances while the wicked are in flourishing ones; and inwardly fret and are uneasy at it, which they should not, Psalm 37:1; or do not "emulate" or "imitate" (z) them, or do as they do, thinking thereby to enjoy the same prosperity and happiness; choose not their ways, nor desire to be with them, to have their company, or be ranked among them, Proverbs 3:31;
but be thou in the fear of the Lord all the day long; let the fear of God be always before thine eyes and in thine heart; be continually in the exercise of fear, which is attended with faith and trust in the Lord; with love and affection to him, and joy and delight in him; be constantly employed in the duties of religion, private and public, which the fear of God includes; and this will be a preservative from envying, murmuring, and fretting at the outward happiness of wicked men; and from joining with them in their evil ways. Aben Ezra, and who is followed by some others, render it, "but emulate or imitate the men that fear the Lord all the day long" (a); be followers of them, and do as they do; let their constant piety and devotion stir up a holy emulation in thee to copy after them and exceed them; but the former sense is best.
(z) "ne aemuletur", Pagninus, Montanus, Tigurine version, Junius et Tremellius, Piscator, Mercerus, Cocceius, Gejerus, Michaelis. (a) "Aemulare virum timentem, Jehovam", Vatablus.

The believer's expectation shall not be disappointed; the end of his trials, and of the sinner's prosperity, is at hand.

(Compare Margin). The prosperity of the wicked is short.

The poet now shows how one attains unto wisdom - the beginning of wisdom is the fear of God:
17 Let not thine heart strive after sinners,
But after the fear of Jahve all the day.
18 Truly there is a future,
And thy hope shall not come to naught.
The lxx, Jerome, the Venet., and Luther, and the Arab. interpreters, render 17b as an independent clause: "but be daily in the fear of the Lord." That is not a substantival clause (cf. Proverbs 22:7), nor can it be an interjectional clause, but it may be an elliptical clause (Fleischer: from the prohibitive אל־תקנא is to be taken for the second parallel member the v. subst. lying at the foundation of all verbs); but why had the author omitted היה dettim? Besides, one uses the expressions, to act (עשׂה), and to walk (הלך) in the fear of God, but not the expression to be (היה) in the fear of God. Thus בּיראת, like בחטּאים, is dependent on אל־תּקנּא; and Jerome, who translates: Non aemuletur cor tuum peccatores, sed in timore Domini esto tota die, ought to have continued: sed timorem Domini tota die; for, as one may say in Latin: aemulari virtutes, as well as aemulari aliquem, so also in Hebrews. קנּא ב, of the envying of those persons whose fortune excites to dissatisfaction, because one has not the same, and might yet have it, Proverbs 3:31; Proverbs 24:1, Proverbs 24:19, as well as of emulation for a thing in which one might not stand behind others: envy not sinners, envy much rather the fear of God, i.e., let thyself be moved with eager desire after it when its appearance is presented to thee. There is no O.T. parallel for this, but the Syr. tan and the Greek ζηλοτυποῦν are used in this double sense. Thus Hitzig rightly, and, among the moderns, Malbim; with Aben Ezra, it is necessary to take ביראת for באישׁ יראת, this proverb itself declares the fear of God to be of all things the most worthy of being coveted.
In Proverbs 23:18, Umbreit, Elster, Zckler, and others interpret the כּי as assigning a reason, and the אם as conditioning: for when the end (the hour of the righteous judgment) has come; Bertheau better, because more suitable to the ישׁ and the אחרית: when an end (an end adjusting the contradictions of the present time) comes, as no doubt it will come, then thy hope will not be destroyed; but, on the other hand, the succession of words in the conclusion (vid., at Proverbs 3:34) opposes this; also one does not see why the author does not say directly כי ישׁ אחרית, but expresses himself thus conditionally.
(Note: The form כּי אם־ does not contradict the connection of the two particles. This use of the Makkeph is general, except in these three instances: Genesis 15:4; Numbers 35:33; Nehemiah 2:2.)
If אם is meant hypothetically, then, with the lxx ἐὰν γὰρ τηρήσῃς αὐτὰ ἔκγονα, we should supply after it תּשׁמרנּה, that had fallen out. Ewald's: much rather there is yet a future (Dchsel: much rather be happy there is...), is also impossible; for the preceding clause is positive, not negative. The particles כּי אם, connected thus, mean: for if (e.g., Lamentations 3:32); or also relatively: that if (e.g., Jeremiah 26:15). After a negative clause they have the meaning of "unless," which is acquired by means of an ellipsis; e.g., Isaiah 55:10, it turns not back thither, unless it has watered the earth (it returns back not before then, not unless this is done). This "unless" is, however, used like the Lat. nisi, also without the conditioning clause following, e.g., Genesis 28:17, hic locus non est nisi domus Dei. And hence the expression כי אם, after the negation going before, acquires the meaning of "but," e.g., 17b: let not thy heart be covetous after sinners, for thou canst always be zealous for the fear of God, i.e., much rather for this, but for this. This pleonasm of אם sometimes occurs where כי is not used confirmatively, but affirmatively: the "certainly if" forms the transition, e.g., 1-Kings 20:6 (vid., Keil's Comm. l.c.), whose "if" is not seldom omitted, so that כי אם has only the meaning of an affirmative "certainly," not "truly no," which it may also have, 1-Samuel 25:34, but "truly yes." Thus כי אם is used Judges 15:7; 2-Samuel 15:21 (where אם is omitted by the Kerı̂); 2-Kings 5:20; Jeremiah 51:14; and thus it is also meant here, 18a, notwithstanding that כי אם, in its more usual signification, "besides only, but, nisi," precedes, as at 1-Samuel 21:6, cf. 5. The objection by Hitzig, that with this explanation: "certainly there is a future," Proverbs 23:18 and Proverbs 23:17 are at variance, falls to the ground, if one reflects on the Hebrews. idiom, in which the affirmative signification of כי is interpenetrated by the confirmative. אחרית used thus pregnantly, as here (Proverbs 24:14), is the glorious final issue; the word in itself designates the end into which human life issues (cf. Psalm 37:37.); here, the end crowning the preceding course. Jeremiah (Jeremiah 29:11) in this sense connects אחרית ותקוה [end and expectation]. And what is here denied of the תּקיה, the hope (not as certain Jewish interpreters dream, the thread of life) of him who zealously strives after the fear of God, is affirmed, at Psalm 37:38, of the godless: the latter have no continuance, but the former have such as is the fulfilling of his hope.