Keep thy heart with all diligence; properly, above all things that have to be guarded, keep or guard thy heart. So Mercerus, Gescnius, Delitzsch, Zockler. This seems to be the right meaning of the phrase, mikkol-mish'mar, rendered in the Authorized Version "with all diligence," mish'mar, from shamar, "to guard," being the object of guarding; that which is to be guarded.
It is as if the teacher said, "Guard riches, property, health, body, everything, in short, in which you have a legitimate interest, or which is advantageous; but before and above everything else, keep a guard on your heart."
The rabbins Jarehi, Ben Ezra, Rashi, however, give a different rendering, "From everything which is to be avoided (ab omni re cavenda) guard thy heart;" but the objection to this is that it ignores the radical meaning of the verb shamar, from which mish'mar is derived, as stated above, which is not that of avoiding, but of guarding.
A third rendering is," Keep thy heart with all keeping;" so the Vulgate, omni custodia serva cor tuum; and the LXX; πασὴ φυλακῇ τήρει σὴν καρδίαν; on which the Authorized Version seems to be based.
Another rendering, similar to the first, except that it gives mish'mar the active signification of guarding instead of the passive one of being kept or guarded, is, "Keep thy heart more than any other keeping (prae omni custodia)."
Origen, 'Hex.;' Field. Again, Aquila and Theodotion render, "Keep thy heart by reason of every commandment ( ἀπὸ παντὸς φυλάγματος)," thus bringing into prominence the occasion and the obligation of keeping the heart, which is that we are so commanded.
Heart (lev); here the affections and the moral consciousness. For out of it are the issues of life. The conjunction "for" introduces the reason. The fact here stated is that the moral conduct of life, its actions and proceedings, are determined by the condition of the heart.
If the heart is pure, the life will be pure; if the heart is corrupt, the life will be corrupt. The heart is here compared with a fountain. The same idea which is affixed to it in its physical sense is also assigned to it in its ethical or moral sense.
Physically, it is the central organ of the body; morally, it is the seat of the affections and the centre of the moral consciousness. From this moral centre flow forth "the issues of life;" i.e. the currents of the moral life take their rise in and flow forth from it, just as from the heart, physically considered, the blood is propelled and flows forth into the arterial system, by which it is conveyed to the remotest extremities of the body.
And as the bodily health depends on the healthy action of the heart, so the moral health depends on and is influenced by the state in which this spring of all action is preserved. Issues; tots'aoth, from yatsar, "to go forth," are the place from which anything goes forth, and hence a fountain.
For "the issues of life," the LXX. reads, ἔξοδοι ζωῆς, the Vulgate; exitus vitae. With this passage compare our Lord's teaching.