John Gill Commentary Isaiah 45:5

"I am Jehovah, and there is none else; besides me there is no God. I will gird thee, though thou hast not known me;" — Isaiah 45:5 (ASV)

I am the Lord, and there is none else Whom you, O Cyrus, for the words are directed to him, ought to own, serve, and worship: there is no God besides me; in heaven or earth, in any of the countries conquered by you, and you rule over; for though there were gods and lords many, so called, these were only nominal fictitious deities; not gods by nature, as he was; of which the following, as well as what is before said, is a proof.

I girded you, though you have not known me; the Lord girded him with a royal girdle, a symbol of kingly power; he made him king over many nations; he girded him with strength, courage, and valour for war; and made him so expeditious, successful, and victorious, as he was, though a Heathen prince, and ignorant of him, in order to answer some valuable ends of his own glory, and the good of his people, and particularly for what follows.