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 Psalms 49:5 in those who were not possessed of it, and who might be subjected to the oppressive acts of those who were rich.