Day unto day - One day to another; or, each successive day. The day that is passing away proclaims the lesson which it had to convey from the movements of the heavens, about God; and thus the knowledge of God is accumulating as the time moves on. Each day has its own lesson in regard to the wisdom, the power, and the goodness of God, and that lesson is conveyed from one day to another. There is a perpetual testimony thus given to the wisdom and power of the Great Creator.
Uttereth speech - The word here rendered uttereth means properly to pour forth; to pour forth copiously as a fountain. Compare Proverbs 18:4; Proverbs 1:23; Proverbs 15:2, Proverbs 15:28. Hence, the word means to utter; to declare. The word “speech” means properly “a word;” and then, “a lesson;” or “that which speech conveys.” The idea is, that the successive days thus impart instruction, or convey lessons about God. The day does this by the returning light, and by the steady and sublime movement of the sun in the heavens, and by all the disclosures which are made by the light of the sun in his journeyings.
And night unto night showeth knowledge - Knowledge respecting God. Each successive night does this. It is done by the stars in their courses; in their order; their numbers; their ranks; their changes of position; their rising and their setting. There are as many lessons conveyed to man about the greatness and majesty of God by the silent movements of each night as there are by the light of the successive days - just as there may be as many lessons conveyed to the soul about God in the dark night of affliction and adversity, as there are when the sun of prosperity shines upon us.