There is no other God
Isaiah 44: 6
"Thus says the Lord, the King of Israel, I am the First and I am the Last; Besides Me there is no God. And who can proclaim as I do? Then let him declare it and set it in order for Me, Since I appointed the ancient people and the things that are coming and shall come. Let them show these to them. Do not fear, nor be afraid; Have I not told you from that time and declared it? You are my witnesses. Is there a God beside Me? Indeed there is no other Rock;I know no one."
In Isaiah the writer describes God as being a jealous God. If it did not matter what you worshiped or believed God would not take the time to tell you that what your doing is wrong. Because when your the Creator you want your creation to acknowledge you. For example as a Father if your daughter ignores you outright you feel terrible especially if you want a relationship. God is the same way, he made you and me and wants a genuine relationship of worship and reverence. What you might say "am I to worship the air, the nothing" In the air is the powers of the universe.. Make sure its the right power.