Better, as in the margin, i. e., with more vigilance than men use over anything else. The words that follow carry on the same similitude. The fountains and wells of the East were watched over with special care. The heart is such a fountain, out of it flow the "issues" of life. Shall men let those streams be tainted at the fountain-head?

Keep thy heart with all diligence - "Above all keeping," guard thy heart. He who knows any thing of himself, knows how apt his affections are to go astray.
For out of it are the issues of life - תוצאות חיים totseoth chaiyim, "the goings out of lives." Is not this a plain allusion to the arteries which carry the blood from the heart through the whole body, and to the utmost extremities? As long as the heart is capable of receiving and propelling the blood, so long life is continued. Now as the heart is the fountain whence all the streams of life proceed, care must be taken that the fountain be not stopped up nor injured. A double watch for its safety must be kept up. So in spiritual things: the heart is the seat of the Lord of life and glory; and the streams of spiritual life proceed from him to all the powers and faculties of the soul. Watch with all diligence, that this fountain be not sealed up, nor these streams of life be cut off. Therefore "put away from thee a froward mouth and perverse lips - and let thy eyes look straight on." Or, in other words, look inwardlook onward - look upward.
I know that the twenty-third verse is understood as principally referring to the evils which proceed from the heart, and which must be guarded against; and the good purposes that must be formed in it, from which life takes its colouring. The former should be opposed; the latter should be encouraged and strengthened. If the heart be pure and holy, all its purposes will be just and good. If it be impure and defiled, nothing will proceed from it but abomination. But though all this be true, I have preferred following what I believe to be the metaphor in the text.

Keep thy heart with all diligence; for out of it [are] the issues of (k) life.
(k) For as the heart is either pure or corrupt, so is the whole course of man's life.

Keep thy heart with all diligence,.... The mind from vanity, the understanding from error, the will from perverseness, the conscience clear of guilt, the affections from being inordinate and set on evil objects, the thoughts from being employed on bad subjects; and the whole from falling into the hands of the enemy, or being the possession of Satan: great diligence had need be used in keeping it, since it is naturally so deceitful and treacherous; a strict eye is to be kept upon it; all the avenues to it to be watched, that nothing hurtful enters, or evil comes out; it is to be kept by all manner of means that can be thought of, by prayer, hearing, reading, meditation; and, above all, by applying to Christ for his grace and Spirit to sanctify, preserve, and keep it. Or, "above all keeping, keep thine heart" (b); though other things are to be kept, and care taken of them, as kingdoms and cities, and towns and families, and treasures and riches; yet the heart above all:
for out of it are the issues of life; of natural life: it is the seat of it, from whence all actions of life are derived; it is, as philosophers say, the first that lives, and the last that dies; and it is the seat of spiritual life the principle of it is formed in it; from whence all spiritual and vital actions flow, and which lead unto and issue in eternal life: as is a man's heart, such is his state now, and will be hereafter; if the heart is quickened and sanctified by the grace of God, the man will live a life of faith and holiness here, and enjoy everlasting life hereafter: and if the heart is right, so will the actions of men be; they are regulated and denominated by it; they will then spring from right principles, and be directed to right ends, and performed with right views; great care therefore should be taken of the heart, since so much depends upon it, and it is so well known to God the searcher of it.
(b) "prae omni custodia", Vatablus, Baynus, Mercerus, Gejerus, Michaelis, Schultens; so Aben Ezra and Ben Melech.

with all diligence--or, "above," or "more than all," custody (compare Margin), all that is kept (compare Ezekiel 38:7), because the heart is the depository of all wisdom and the source of whatever affects life and character (Matthew 12:35; Matthew 15:19).

After this general preface the exhortation now becomes special:
23 Above all other things that are to be guarded, keep thy heart,
For out from it life has its issues.
24 Put away from thee perverseness of mouth,
And waywardness of lips put far from thee.
25 Thine eyes should look straight forward,
And thine eyelids look straight to the end before thee.
26 Make even the path of thy feet,
And let all thy ways be correct.
27 Turn not aside to the right and to the left;
Remove thy foot from evil.
Although משׁמר in itself and in this connection may mean the object to be watchfully avoided (cavendi) (vid., under Proverbs 2:20): thus the usage of the language lying before us applies it, yet only as denoting the place of watching or the object observandi; so that it is not to be thus explained, with Raschi and others: before all from which one has to protect himself (ab omni re cavenda), guard thine heart; but: before all that one has to guard (prae omni re custodienda), guard it as the most precious of possessions committed to thy trust. The heart, which according to its etymon denotes that which is substantial (Kernhafte) in man (cf. Arab. lubb, the kernel of the nut or almond), comes here into view not as the physical, but as the intellectual, and specially the ethical centrum.

Heart - Thy thoughts, will, and affections. For - From thence proceed all the actions, as of the natural, so of the spiritual life, which lead to eternal life.