In preaching "trust in God" the moralist anticipates the teaching that man is justified by faith. To confide in God's will, the secret of all true greatness, is to rise out of all our anxieties and plans and fears when we think of ourselves as the arbiters of our own fortunes, and so "lean to our own understanding."

Trust in the Lord with all thine heart - This is a most important precept:
1. God is the Fountain of all good.
2. He has made his intelligent creatures dependent upon himself.
3. He requires them to be conscious of that dependence.
4. He has promised to communicate what they need.
5. He commands them to believe his promise, and look for its fulfillment.
6. And to do this without doubt, fear, or distrust; "with their whole heart."
Lean not unto thine own understanding - אל תשען al tishshaen, do not prop thyself. It is on God, not on thyself, that thou art commanded to depend. He who trusts in his own heart is a fool.

Trust in the Lord with all thine heart,.... Not in a creature, the best, the holiest, and the highest; not in any creature enjoyment, as riches, strength, and wisdom; nor in any outward privilege, arising from natural descent and education; not in a man's self, in his own heart, which is deceitful; nor in any works of righteousness done by him; not in a profession of religion, or the duties of it, ever so well performed; not in frames, nor in graces, and the exercise of them; no, not in faith or trust itself: but in the Lord, the object of all grace, and in him only; in Jehovah the Father, as the God of nature and providence, for all temporal blessings; and as the God of all grace, for all spiritual blessings, and all the needful supplies of grace; and for eternal happiness, which he has provided, promised, and freely gives. Trust in him at all times; in times of affliction, temptation, and darkness: there is a great deal of reason for it; all power and strength are in him to help; his love, grace, and mercy, move him to it, and are always the same: the consideration of what he has done for others that have trusted in him, and for ourselves in times past, should induce and encourage to it; as also the happiness of those that trust in him, who enjoy peace and safety; and his displeasure at those that show any diffidence of him, or distrust him. Trust in Jehovah the Son; in his person for acceptance; in his righteousness for justification; in his blood for pardon; in his fulness for supply; in his power for protection and preservation; and in him alone for salvation and eternal life. Trust in Jehovah the Spirit, to carry on and finish the work of grace upon the heart; of which a saint may be confident that where it is begun it will be completed. And this trust in Father, Son, and Spirit, should be "with all the heart", cordial and sincere. The phrase denotes not so much the strength of faith as the sincerity of it; it signifies a faith unfeigned; it is not saying, or professing, that a man believes and trusts in the Lord; but it is with the heart, and with his whole heart, that he believes unto righteousness, if he believes aright; see Romans 10:10;
and lean not unto thine own understanding; or trust not to that; for it stands opposed to trusting in the Lord. Men should not depend upon their own wisdom and understanding, in the conduct of civil life, but should seek the direction and blessing of Providence, or otherwise will meet with disappointment; and, when they succeed, should ascribe it not to their own prudence and wisdom, but to the goodness of God; for "bread" is not always "to the wise, nor riches to men of understanding", Ecclesiastes 9:11; and much less should men lean to their own understanding in matters of religion; a natural man has no understanding of spiritual things, of the things of the Gospel, nor indeed any practical understanding of things moral, Romans 3:11, Jeremiah 4:22. The understanding of man is darkened by sin; yea, is darkness itself; it is like the first earth, covered with darkness, till light is let into it, and therefore not to be leaned unto and depended on, Ephesians 4:18. There is a necessity of a new heart and spirit, of an understanding to be given, in order to understand spiritual and divine things, Ezekiel 36:26; for though these are not contrary to the reason and understanding of men; yet they are above them, and cannot be discovered, reached, comprehended, and accounted for by them, Matthew 16:17. Nay, there are some things in the Gospel, which, though plain to an enlightened understanding by the word of God, yet the manner how they are cannot be apprehended: as the doctrines of a trinity of Persons; of the generation of the Son of God; the procession of the Spirit; the union of the two natures in Christ; the resurrection of the dead, &c. In short, not our reason and understanding at best, and much less as carnal and unsanctified, but the word of God only is our rule of judgment, and the standard of our faith and practice; and to that we should have recourse and be directed by it, and not lean to our own understandings.

Trust . . . heart--This is the center and marrow of true wisdom (Proverbs 22:19; Proverbs 28:25). The positive duty has its corresponding negation in the admonition against self-confidence.

Were "kindness and truth" (Proverbs 3:3) understood only in relation to men, then the following admonition would not be interposed, since it proceeds from that going before, if there the quality of kindness and truth, not only towards man, but also towards God, is commended:
5 Trust in Jahve with thy whole heart,
And lean not on thine own understanding.
6 In all thy ways acknowledge Him,
And He will make plain thy paths.
7 Be not wise in thine own eyes;
Fear Jahve, and depart from evil.
8 Health will then come to thy navel,
And refreshing to thy bones.
From God alone comes true prosperity, true help. He knows the right way to the right ends. He knows what benefits us. He is able to free us from that which does us harm: therefore it is our duty and our safety to place our confidence wholly in Him, and to trust not to our own judgment. The verb בּטח, Arab. baṭḥ, has the root-meaning expandere, whence perhaps, by a more direct way than that noted under Psalm 4:6, it acquires the meaning confidere, to lean with the whole body on something, in order to rest upon it, strengthened by על, if one lean wholly - Fr. se reposer sur quelqu'un; Ital. riposarsi sopra alcuno, - like השּׁען with אל, to lean on anything, so as to be supported by it; with על, to support oneself on anything (Fl.). דעהוּ (the same in form as שׂאהוּ, Numbers 11:12) is not fully represented by "acknowledge Him;" as in 1-Chronicles 28:9 it is not a mere theoretic acknowledgment that is meant, but earnest penetrating cognizance, engaging the whole man. The practico-mystical דעהוּ, in and of itself full of significance, according to O. and N.T. usage, is yet strengthened by toto corde. The heart is the central seat of all spiritual soul-strength; to love God with the whole heart is to concentrate the whole inner life on the active contemplation of God, and the ready observance of His will. God requites such as show regard to Him, by making plain their path before them, i.e., by leading them directly to the right end, removing all hindrances out of their way. ארחתיך has Cholem in the first syllable (vid., Kimchi's Lex.).
(Note: In the st. constr. Proverbs 2:19, and with the grave suff. Proverbs 2:15, ǒ instead of ō is in order; but Ben-Asher's ארחתי, Job 13:27, cf. Job 33:11, is an inconsistency.)
"Be not wise in thine own eyes" is equivalent to ne tibi sapiens videare; for, as J. H. Michaelis remarks, confidere Deo est sapere, sibi vero ac suae sapientiae, desipere. "Fear God and depart from evil" is the twofold representation of the εὐσέβεια, or practical piety, in the Chokma writings: Proverbs 16:6, the Mashal Psalm 34:10, Psalm 34:15, and Job 28:28 cf. Proverbs 1:2. For סר מרע, the post-biblical expression is ירא חטא.

Trust - Wholly rely upon God's promises and providences. Lean not - Under this one kind of carnal confidence, he understands all other confidence in bodily strength, wealth, or friends.