Everything we know about the world is experienced through our consciousness, and that includes the material reality of the world around us. So it makes more sense to doubt the existence of the material world than it does to doubt our own consciousness.
What does it mean for consciousness to be an “emergent property” of the brain? As Hoffman says there is not really any scientific theory to account for this. Material and consciousness are apparently two different things and it is utterly mysterious how one relates to the other. It’s as if playing music somehow results in a lemon cake. It’s utterly unclear how the two things, the physical body and consciousness, are fundamentally connnected to each other.
I know that I exist as a conscious entity because I feel this directly. I only know about the material world second hand, through perception, and listening to others.
Maybe the material world does exist independently of us. But the other option is that the material world is an “emergent property” (again whatever that means) of our consciousness. It’s not how we normally view reality, but it’s not easy to say that a materialist basis of reality should necessarily be given priority over the view that consciousness is basic to reality and the material is a result of consciousness rather than the other way round.