John Gill Commentary Daniel 2:45

"Forasmuch as thou sawest that a stone was cut out of the mountain without hands, and that it brake in pieces the iron, the brass, the clay, the silver, and the gold; the great God hath made known to the king what shall come to pass hereafter: and the dream is certain, and the interpretation thereof sure." — Daniel 2:45 (ASV)

Forasmuch as you saw that the stone was cut out of the mountain without hands (See Gill on Daniel 2:34) and that it broke in pieces the iron, the brass, the clay, the silver, and the gold;

of which the image was made he had seen in his dream; and which represented the several monarchies of the world in succession, and described their nature, condition, and circumstances, and the ruin of them; (See Gill on Daniel 2:35).

the great God has made known to the king what shall come to pass hereafter; after his own death, and in his own monarchy; and what will be the fate of succeeding ones; what will come to pass in each of the ages of time, and what will be done in the last days; what an everlasting kingdom there will be, when the kingdoms of this world shall be no more; and this the "great" God, who is great in knowledge as well as power, made known to him, which none else could; and by which he appears to be great, and above all gods, as Nebuchadnezzar afterwards owns; and which Daniel here suggests to him; see (Isaiah 45:21) (Isaiah 46:9Isaiah 46:10) :

and the dream is certain, and the interpretation thereof sure; this is certainly the dream the king had dreamed, for the truth of which he appeals to him; and the interpretation of it given would be most surely and faithfully accomplished, on which he might depend; for since the dream had been so distinctly related to him, he had no room to doubt of the true interpretation of it.