8. This book of the Law, etc Assiduous meditation on the Law is also commanded; because, whenever it is intermitted, even for a short time, many errors readily creep in, and the memory becomes rusted, so that many, after ceasing from the continuous study of it, engage in practical business, as if they were mere ignorant tyros. God therefore enjoins his servant to make daily progress, and never cease, during the whole course of his life, to profit in the Law. Hence it follows that those who hold this study in disdain, are blinded by intolerable arrogance.
But why does he forbid him to allow the Law to depart from his mouth rather than from his eyes? Some interpreters understand that the mouth is here used by synecdoche for face; but this is frigid. I have no doubt that the word used is peculiarly applicable to a person who was bound to prosecute the study in question, not only for himself individually, but for the whole people placed under his rule. He is enjoined, therefore, to attend to the teaching of the Law, that in accordance with the office committed to him, he may bring forward what he has learned for the common benefit of the people. At the same time he is ordered to make his own docility a pattern of obedience to others. For many, by talking and discoursing, have the Law in their mouth, but are very bad keepers of it. Both things, therefore, are commanded, that by teaching others, he may make his own conduct and whole character conformable to the same rule.
What follows in the second clause of the verse shows, that, everything which profane men endeavor to accomplish in contempt of the word of God, must ultimately fail of success, and that however prosperous the commencement may sometimes seem to be, the issue will be disastrous; because prosperous results can be hoped for only from the divine favor, which is justly withheld from counsels rashly adopted, and from all arrogance of which contempt of God himself is the usual accompaniment. Let believers, therefore, in order that their affairs may turn out as they wish, conciliate the divine blessing alike by diligence in learning and by fidelity in obeying.
In the end of the verse, because the term used is ambiguous, as I have already observed, the sentence is repeated, or a second promise is added. The latter is the view I take. For it was most suitable, that after the promised success, Joshua should be reminded that men never act skillfully and regularly except in so far as they allow themselves to be ruled by the word of God. Accordingly, the prudence which believers learn from the word of God, is opposed to the confidence of those who deem their own sense sufficient to guide them aright. (23)
(23) The French paraphrases the whole sentence thus: “ Ainsi la prudence et sagesse que les fideles apprennent de la parole de Dieu, est opposee a l’assurance de ceux auxquels il semble bien qu’ils se gouvernent assez discretement et sagement, quand ils besongnent selon leur propre sens;” “Thus the prudence and wisdom which believers learn from the word of God, is opposed to the assurance of those who think they govern themselves discreetly and wisely enough, when they manage according to their own sense.” — Ed.