My mouth shall speak of wisdom The prophet was warranted in applying these commendatory terms to the doctrine which he was about to communicate. It is, no doubt, by plain appeals to observation that we find him reproving human folly; but the general principle upon which his instruction proceeds is one by no means obvious to the common sense of mankind, not to say that his design in using such terms is less to assert the dignity of his subject than simply to awaken attention. This he does all the more effectually by speaking as one who would apply his own mind to instruction rather than assume the office of exhortation. He puts himself forward as an humble scholar, one who, in acting the part of teacher, has an eye at the same time to his own improvement. It were desirable that all the ministers of God should be actuated by a similar spirit, disposing them to regard God as at once their own teacher and that of the common people, and to embrace in the first place themselves that divine word which they preach to others. [1] The Psalmist had another object in view. He would secure the greater weight and deference to his doctrine by announcing that he had no intention to vend fancies of his own, but to advance what he had learned in the school of God. This is the true method of instruction to be followed in the Church. The man who holds the office of teacher must apply himself to the reception of truth before he attempt to communicate it, and in this manner become the means of conveying to the hands of others that which God has committed to his own. Wisdom is not the growth of human genius. It must be sought from above, and it is impossible that any should speak with the propriety and knowledge necessary for the edification of the Church, who has not, in the first place, been taught at the feet of the Lord. To condescend upon the words, some read in the third verse, And the meditation of my heart shall speak of understanding But as it were a harsh and improper expression to say that the meditation of the heart speaks, I have adopted the simpler reading.

Footnotes

1 - "Aussi certes il est bien requis que tous les Prophetes de Dieu ayent un tel vouloir et affection, ascavoir qu'ils souffrent volontiers que Dieu soit leur maistre aussi bien que de tout le peuple, et qu'ils recoyvent tous les premiers sa parolle, laquelle ils portent de leur bouche aux autres." -- Fr.

My mouth shall speak of wisdom - That is, I will utter sentiments that are wise, or that are of importance to all; sentiments that will enable all to take a just view of the subject on which I speak. This indicates "confidence" in what he was about to utter, as being eminently deserving of attention.
And the meditation of my heart shall be of understanding - What I reflect on, and what I give utterance to, in the matter under consideration. The idea is, that he had meditated on the subject, as to what was real wisdom in the matter, and that he would now give utterance to the result of his meditations. It was not wisdom in general, or intelligence or understanding as such on which he designed to express the results of his thoughts, but it was only in respect to the proper value to be attached to wealth, and as to the fact of its causing fear Psalm 49:5 in those who were not possessed of it, and who might be subjected to the oppressive acts of those who were rich.

My mouth shall speak of wisdom,.... Or "wisdoms" (m); of Christ, who is so called, Proverbs 1:20. He being as a divine Person the wisdom of God, and the only wise God; and having all the treasures of wisdom in him, as man and Mediator: of him the prophet spake, and of him the apostles and all Gospel ministers speak; of the glories of his Person, of the fulness of his grace, and of his wonderful works; especially of that of redemption and salvation by him, in which there is an abounding of wisdom and prudence. Or the Gospel may be meant, and all the truths of it, in which there is a glorious display of divine wisdom; it is the wisdom of God in a mystery; hidden and ancient wisdom; and which, when truly understood, makes a man wise unto salvation; see 1-Corinthians 2:6;
and the meditation of my heart shall be of understanding; or "understandings" (n); and this is in order to the former; what the heart meditates the mouth speaks. If the heart meditates on understanding, the mouth will speak of wisdom; and a man should think before he speaks, especially the ministers of the Gospel: they ought to meditate on the word of God, the Gospel, and the truths of it, that their profiling may appear to all; that they may understand divine things themselves, and deliver them out to the understanding of others: their concern should be, that through meditation they may have a good treasure of wisdom and knowledge in their hearts, that out of it they may bring forth things pleasant and profitable unto others.
(m) "sapientias", Pagninus, Montanus, Vatablus, Cocceius, Gejerus, Michaelis. (n) "intelligentias", Pagninus, Montanus.