Isaiah 45:1-7 Thus says the LORD to His anointed, To Cyrus, whose right hand I have held— To subdue nations before him And loose the armor of kings, To open before him the double doors, So that the gates will not be shut: 'I will go before you And make the crooked places straight; I will break in pieces the gates of bronze And cut the bars of iron. I will give you the treasures of darkness And hidden riches of secret places, That you may know that I, the LORD, Who call you by your name, Am the God of Israel. For Jacob My servant's sake, And Israel My elect, I have even called you by your name; I have named you, though you have not known Me. I am the LORD, and there is no other; There is no God besides Me. I will gird you, though you have not known Me, That they may know from the rising of the sun to its setting That there is none besides Me. I am the LORD, and there is no other; I form the light and create darkness, I make peace and create calamity; I, the LORD, do all these things.
This passage refers to Cyrus, King of Media and Persia, who would conquer Babylon and set the Jews free to return to Babylon. The passage in question indicates that God would remove all obstacles of conquest from before Cyrus because Cyrus would be God's instrument in the outworking of His purpose with Israel. The phrase, "I form the light and create darkness" references the Zoroastrian religion of Persia where there were two gods - the god of goodness and light, Ahura Mazda, and the god of evil and darkness, Ahriman. God declares that there is no such duality in the universe. He is God alone.
I hope you have found this helpful.