Great is our Lord - See the notes at Psalm 48:1.
And of great power - This seems to be added, as in Isaiah 40:28, in view of the power required in making the heavens, and in guiding and numbering the stars: "Hast thou not known? Hast thou not heard, that the everlasting God, the Lord, the Creator of the ends of the earth, fainteth not, neither is weary?"
His understanding is infinite - Margin, Of his understanding there is no number. That is, This corresponds with his power to number the stars. There is no limit to it. It is not bounded; there is no point reached where it can be said that there is no more; that it is exhausted. See the notes at Isaiah 40:28 : "There is no searching of his understanding."

His understanding is infinite - To his intelligence there is no number: though he numbers the stars, his understanding is without number. It is infinite; therefore, he can know, as he can do, all things.

Great is our Lord, and of great power,.... "Our Lord" is our Lord Jesus Christ, the Lord of the whole earth; the Lord of his own people by creation, by redemption, by marriage, and by the conquest of his grace, and their voluntary submission to him; he is "great" in his person, offices, and grace, and therefore greatly to be praised; see Psalm 145:3; and particularly his "power" is very "great", as appears in the creation of all things out of nothing by him; in the sustaining and support of the world and all things in it: in the redemption of his people from the hand of their powerful enemies; in beginning, carrying on, and perfecting a work of grace on their hearts by his Spirit and power; and in the preservation of them unto eternal life, through a thousand dangers and difficulties: at his resurrection all power in heaven and earth were given him as Mediator; and in the latter day he will take to himself his great power and reign; and in the last day will raise the dead out of their graves;
his understanding is infinite; it reaches to all things, not to the stars of heaven only, as in Psalm 147:4, but to the fowls of the air, to the beasts of the field, and cattle upon a thousand hills; to all on the surface of the earth, or in the bowels of it; and to the fishes of the sea: it reaches to all men, and to all the thoughts of their hearts, the words of their mouths, and the actions of their lives; it reaches to all things past, that have been, to everything present, and to whatsoever is to come; it includes not only the knowledge of all things that are, or certainly will be, but of all things possible, or which he could bring into being if he would; it is concerned not only with the quality and nature of things it perfectly understands, but with the quantity of them; even all things in creation and providence, which are without number and past finding out by men; and so his understanding is without number, and cannot be declared, as the word signifies.