This puts me on a tangent.....If God is the most-powerful, then satan cannot be equally powerful. Why does satan exist?
Part of a heavenly Make-Work Program, so that unemployment numbers drop, and God's re-election campaign looks better? ;0)
(j/k)
God is most powerful. He is the creator and sustainer of the universe. There are many attributes of God that are unique. For example, His perfection, omnipotence, immortality, power and omnipresense. Also, God was not created. He has always existed.
Satan was created by God as the angel Lucifer. Lucifer decided that he wanted to be God and rebelled against his creator. There was a battle and Lucifer lost and was cast out of heaven along with 1/3 of the angels that had followed him.
Lucifer's fall was the result of his own sin against God. That is why Satan exists. Note that Satan is a created being and does not have the attributes of God listed above. God has no peer because all other beings were created by him.
The satan is a manifestation of G-d's will. There is no power or force greater or equal to G-d. And the fact that G-d knows the past, present, and future, doesn't mean we don't have free will. Tomorrow if you go to Baskin Robbins and order chocolate ice cream when you usually order vanilla, G-d isn't going to go, 'doh, I thought he was going to order vanilla.' G-d was already there and knows you ordered chocolate. It doesn't mean you didn't have the free will to choose chocolate or vanilla. Get it? It's complicated.
Satan exists precisely because God gave all His creatures free will and He does not force them to behave in any way. They are FREE to choose not to follow God's laws, that is, to become like Satan.
Satan provides the critical opposition required for there to be a freedom of choice. If there was nothing to choose but good, how could we honestly expect to be rewarded? Those who are rewarded of God are those who are given a real alternative, opportunities to choose something else, and yet choose to give obedience and glory to Him.