My words [shall be of] the uprightness of my heart
Not that the uprightness of his heart, or his own personal integrity, should be the subject of his discourse; but what he should say would be in or out of the uprightness of his heart, with all sincerity and faithfulness; what would be the real sentiments of his mind, and not proceed from a double or insincere heart:
and my lips shall utter knowledge clearly;
what knowledge he had of God, and of the perfections of his nature, and of his works in nature and grace, and of his dealings in a providential way with the sons of men; and what knowledge he had of Christ, his person, office, and grace somewhat of which speaks in this chapter; and such sort of knowledge is to be uttered, to be published, and made known to the good of others; and not to be concealed, and hid, or held, as in a prison, in unrighteousness; and to be uttered clearly, plainly, and distinctly, in words intelligible, and easy to be understood; and not in ambiguous terms, or in words of a double meaning; or which are abstruse and intricate, and serve rather to make the mysteries of Providence and grace more dark and obscure than to explain them; integrity of heart, and perspicuity of language, serve much to recommend a speaker, and both are expressed in this verse.