So as not to bore you with today's modern explanation as to why we dream (google it), I'll give you an explanation that is coherent to everything THC have shared up to this point. Here goes it:
Our Theory Dreams are designed to be a balancing opposite to your awaken state.
Think about it, every motion is eventually met with stillness, and every life is eventually met with death. The two YIN&YANG is what we call DUALITY, a concept that is most fundamental to understanding the whole of Universe, and not just its parts; the Metaphysical, and not just the Physical.
Contrasting to that is your Dream State.
The list would be unending if we choose to compare and contrast both states. Personally, I find it quite anti-climatic and boring to compare the two state. No matter how I spin it, there's no denying the principles of Duality and how the Universe have nestled this principle into each and every dimension of our existence; 'cause literally, everything we know to be -- relationship, entertainment, health, wealth, self-awareness, etc -- could be framed in terms of duality, polarity, and relativity. So, if the awaken state is mostly a coherent one, then our dream state has to be one plagued of incoherence.
We can't run from our need for balance. It's inescapable.