Why are we able to have lucid dreams? What purpose do they serve? Why are we able to control dreams? Why is the level of control always different?

Most of what our minds can do is necessary to our lives somehow. We need certain functions, so we have them.

We're already able to daydream. Lucid dreaming, with control, is just a step beyond daydreaming - you can interact with your fantasy first hand.

But then, you can't change the situation as quickly as you can in a daydream. You can quickly "play out" several different ways something can happen in a daydream. Changing the scene in a dream is much more difficult, if not impossible for most people.

So why have the ability at all? Why don't more people have lucid dreams? Why do so many conditions have to sometimes be met for one to experience a lucid dream (such as going to bed early, using audio and visual cues during sleep, etc.)?

Could lucid dreaming be a beginning stage of the evolution of a "higher function?" If it is, it'll be something else that I won't live to experience.

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In sleep, fantasy takes the form of dreams. But in waking life, too, we continue to dream beneath the threshold of consciousness, especially when under the influence of repressed or other unconscious complexes. -- C. G. Jung, "Problems of Modern Psychotherapy" (1929). In CW 16: The Practice of Psychotherapy. pg. 125