Most dreams are just expressions of the subconscious mind of the dreamer, which is supressed during waking hours. Subconscious desires and fears come to the surface during rapid eye movement sleep and get expressed in the dreamer’s mind, either realistically or symbolically. That’s psychoanalytic and brain biology theory, anyways. There isn’t necessarily any real meaning to most of them, just that your brain is working out something you don’t attend to often during wakefulness. You miss your parents, and dream of them. What they say to you may be about some issue you’ve been thinking about when you’re awake. Some medications, alcohol, and even some foods can interfere with dreaming, because they interfere with the rapid eye movement phase.
I’d think that the content of dreams is pretty wildly variable, and it’s all of God’s permissive will, since He designed our brains to go through this dream phase every night, whether the content makes any sense or not, or even whether we remember the content of the dreams. Since a lot of critical biologic things in the rest of our bodies go on during that phase of sleep, like muscle repair and increased immune response, it’s pretty clear that God wants us to be able to dream. If yours are pleasant, so much the better.