If you don't like the only God there is, you can always make up your own and believe in him or her. What do you think? I mean, you can do that, just like you can wait in line for an invisible ride at the amusement park, hoping to ride it. You say, "No one does that." Most people do that with God. They shape a god in their minds to fit their desires. Religions or churches encourage this too. People fill up buildings to and for a god that doesn't exist. There is a point when actual God dips below His actual identity in people's imagination, so that He isn't God anymore.
Let's say a very strong, large, tough man in an official uniform, because he's in authority, tells you that you've got to eat two fried eggs and two slices of whole wheat, buttered toast every morning, or he'll plaster you in the nose with his fist. In your mind, he doesn't exist, so you eat oatmeal instead. I guess he was real, as seen in your broken, bleeding nose. The next morning you try two pieces of fruit and then welcome his fist again. It doesn't seem you can just wish him away. He's real. The next morning it is two fried eggs and two slices of whole wheat, buttered toast, no fist in your nose either.
Your thoughts and the acknowledgement and belief about God must portend with reality. You can't imagine Him to be who you want Him to be and then count a response to Him as God to count as one. God has to be God.
People worship the God of their imagination. For Him to be God, the imagination must be shaped by and then conform to the truth. If not, He isn't Him. You can say you are worshiping Him, but you are not. You can say He will save you, and He won't. You can say that you are safe from God's judgment, but you are not. You can say that you are waiting for a ride at the amusement park, but it must exist for you to do that.
The nation Israel started off with God, or what we could call the One, True God. There is only One, so someone can just call Him God. God revealed Himself. After awhile, in general Israel didn't like their God, Who was the only God. Even though there isn't another one, they wanted another one, or at least the One they had, the true One, to be different than Who He actually was. They began worshiping their God like one of the other ones, which were gods of their roundabout neighbors.
By the time we get to Jesus in the gospels, the Samaritans, who were partly Jewish, were worshiping a god about which Jesus said in John 4:22, "Ye worship ye know not what." Later, when the Apostle Paul wrote to the Romans, you could say that they were in a similar circumstance, when he told the Jews there in the audience in Romans 10:2, "For I bear them record that they have a zeal of God, but not according to knowledge." At Corinth, the imagination of Jesus had been so distorted, that Paul wrote professing believers there in 1 Corinthians 12:3, claiming to be "speaking by the Spirit of God," "calleth Jesus accursed." In their ecstatic state, they thought that true about Jesus, and accused the Holy Spirit of revealing that lie to them about Jesus as well.
The nation Israel started with the right knowledge, but that knowledge became distorted as Israelites, Jews, began to conform God in their minds to their own desires. They would match up to God in their own righteousness, so His righteousness must be something where theirs could do that. They diminished God's righteousness with the thought that He would see theirs as acceptable. They wouldn't have to submit to the righteousness of the new god of their imagination. They could establish their own righteousness as good enough and be saved by works. God wasn't God anymore in their imagination. The god that replaces God is an idol. They are worshiping an idol, an idol that accepts their behavior, which is less than what actual God accepts.
Most people have a different god today with whom they are satisfied with. They serve him in their own way. They obey him like they like to obey. He saves them like they want to be saved. He's not real. In the end, the one, only True God will give them the equivalent of the metaphorical fist in the nose of the above illustration in paragraph two. They'll know Who He is right at that moment, but it will be too late.
If we can't take the only God at His Word, we won't believe in Him. When we won't or can't believe, we won't or can't be saved. God has to be God.