Christians: Explain this to me.?

I am not sure what religion I am, and I do not hate christians, I once was a devout one myself, but How do you base your life off of a book that say the earth is a flat piece of land with a dome over it and water that flows through gates to make it rain? I know you say it is just a "Truth", but all christians once fully believed it. As science advances further, will you still keep saying "Oh, no, it meant that!", because a book "guided by god" shouldn't say thing like the earth is flat. I don't understand. I'm not a hater, just curious.