For thou shalt light my lamp. In the song in Samuel, the form of the expression is somewhat more precise; for there it is said not that God lights our lamp, but that he himself is our lamp. The meaning, however, comes to the same thing, namely, that it was by the grace of God that David, who had been plunged in darkness, returned to the light. David does not simply give thanks to God for having lighted up a lamp before him, but also for having converted his darkness into light. He, therefore, acknowledges that he had been reduced to such extremity of distress, that he was like a man whose condition was forlorn and hopeless; for he compares the confused and perplexed state of his affairs to darkness. This, indeed, by the transference of material things to things spiritual, may be applied to the spiritual illumination of the understanding; but, at the same time, we must attend to the subject of which David treats, that we may not depart from the true and proper meaning. Now, as he acknowledges that he had been restored to prosperity by the favor of God, which was to him, as it were, a life-giving light, let us, after his example, regard it as certain that we will never have the comfort of seeing our adversities brought to an end, unless God disperse the darkness which envelops us, and restore to us the light of joy. Let it not, however, be distressing to us to walk through darkness, provided God is pleased to perform to us the office of a lamp. In the following verse, David ascribes his victories to God, declaring that, under his conduct, he had broken through the wedges or phalanxes of his enemies, and had taken by storm their fortified cities. [1] Thus we see that, although he was a valiant warrior, and skilled in arms, he arrogates nothing to himself. As to the tenses of the verbs, we would inform our readers once for all, that in this psalm David uses the past and the future tenses indifferently, not only because he comprehends different histories, but also because he presents to himself the things of which he speaks as if they were still taking place before his eyes, and, at the same time, describes a continued course of the grace of God towards him.

Footnotes

1 - The last clause, By my God have I leaped over a wall, is rendered by the Chaldee, "I will subdue fortified towers." Hammond renders it, "By my God I have taken a fort." In support of this view, he observes that the word svr, shur, from svr, shor, to look, signifies both a wall, from which to observe the approach of the enemy, and a watch-tower and fort; that if we take svr, shur, as meaning a wall, the verb dlg, dalag, will be rightly rendered to leap over; but if svr, shur, means a fort, then the verb will mean to seize on it suddenly, and will therefore be best translated to take it.

For thou wilt light my candle - Margin, lamp. The word lamp best expresses the idea. In the Scriptures light is an image of prosperity, success, happiness, holiness, as darkness is the image of the opposite. See the notes at Job 29:2-3; compare also Job 18:6; Job 21:17; Proverbs 20:27; Proverbs 24:20; Psalm 119:105; Psalm 132:17; Isaiah 62:1. The meaning here is, that the psalmist felt assured that God would give him prosperity, as if his lamp were kept constantly burning in his dwelling.
The Lord my God will enlighten my darkness - Will shed light on my path, which would otherwise be dark: will impart light to my understanding; will put peace and joy in my heart; will crown me with his favor. Compare the note at Psalm 4:6.

For thou wilt light my candle - Thou wilt restore me to prosperity, and give me a happy issue out of all my afflictions. By the lamp of David the Messiah may be meant: thou wilt not suffer my family to become extinct, nor the kingdom which thou hast promised me utterly to fail.

For thou wilt light my candle,.... Or lamp (d): in 2-Samuel 22:29, it is, "Thou art my lamp, O Lord"; which may either design outward prosperity, and the flourishing condition of David's kingdom; or internal spiritual light, and an increase of it, by giving fresh supplies of the oil of grace, to cause the lamp to burn more clearly; or rather the prosperous estate of Christ's kingdom; and may be the same with the lamp ordained for the Messiah, Psalm 132:17;
the Lord my God will enlighten my darkness; or "cause light to shine in my darkness" (e); that is, bring me out of darkness into light; either out of adversity to prosperity, or from walking in darkness to the enjoyment of the light of his countenance; and is true of Christ, not only of the prosperity of his kingdom and interest, but of him personally; who though, when on the cross, was in darkness of soul, being forsaken by his God; yet, when raised from the dead, he was received up to heaven, and set down at the right hand of God, and was made full of joy with his countenance, Acts 2:28.
(d) "lucernam meam", Pagninus, Montanus, Junius & Tremellius, Piscator, &c. (e) So Gussetius, Comment. Ebr. p. 495.

To give one light is to make prosperous (Job 18:5-6; Job 21:17).
thou--is emphatic, as if to say, I can fully confide in Thee for help.

(Hebrews.: 18:29-31) The confirmation of what has been asserted is continued by David's application of it to himself. Hitzig translates the futures in Psalm 18:29. as imperfects; but the sequence of the tenses, which would bring this rendering with it, is in this instance interrupted, as it has been even in Psalm 18:28, by כּי. The lamp, נר (contracted from nawer), is an image of life, which as it were burns on and on, including the idea of prosperity and high rank; in the form ניר (from niwr, nijr) it is the usual figurative word for the continuance of the house of David, 1-Kings 11:36, and frequently. David's life and dominion, as the covenant king, is the lamp which God's favour has lighted for the well-being of Israel, and His power will not allow this lamp (2-Samuel 21:17) to be quenched. The darkness which breaks in upon David and his house is always lighted up again by Jahve. For His strength is mighty in the weak; in, with, and by Him he can do all things. The fut. ארץ may be all the more surely derived from רצץ (= ארץ), inasmuch as this verb has the changeable u in the future also in Isaiah 42:4; Ecclesiastes 12:6. The text of 2 Sam 22, however, certainly seems to put "rushing upon" in the stead of "breaking down." With Psalm 18:31 the first half of the hymn closes epiphonematically. האל is a nom. absol., like hatsuwr, Deuteronomy 32:4. This old Mosaic utterance is re-echoed here, as in 2-Samuel 7:22, in the mouth of David. The article of האל points to God as being manifest in past history. His way is faultless and blameless. His word is צרוּפה, not slaggy ore, but purified solid gold, Psalm 12:7. Whoever retreats into Him, the God of the promise, is shielded from every danger. Proverbs 30:5 is borrowed from this passage.

Lightest - Given me safety, and comfort, and glory, and posterity also.