One of those ways, the brain takes care of daily business, is by softly shuting down as we sleep. I say 'softly' because it never really sleeps. It does slow down while we sleep.
In that state, the brain is able to take the time to file things away.
Just like the computer you're using right now, your brain must file things away in appropriate manners. What might make sense to you while awake, might not make sense anymore when the brain gets hold of it for filing. Which explains some pretty weird dreams.
Dreams come in all sorts of forms. Some are simply emotional settling, some are the brain searching for solutions, some are prophetic in nature, some are direct messages from the Lord Himself.
