why humankind dream in night?

Cause it's hard to sleep on daytime?

Because that's when humankind sleeps.

A person can better know the meanings of dreams that have meanings by practicing true devotion to Gabriel the Archangel, who is the patron of messengers and postal workers, and was the guardian angel for the Virgin Mary during her natural life.

in night-dream, humankind happened many accidents.
after awaking, people remember little happening.
why that happening tooks place?
really, thy got a good sleep last night.
today i try to remember accident happened last dream.
by the way, this morning, i haven't fresh feeling, and do glooomy.
of course, in dream. there were both dream-explanation.
as it were, good or bad explanation of dream.
here, i would like to raise a doubt about dream.
whether dream is the free will of humankind or not?
surely, dream is the sleeping brain-activity.
if so that, sleeping has seocond reaction of brain.
because humankind can't react or response outside environment in sleeping,
and be block from outside stimulus.
hence, sleeping-dream can not but seeing only brain-activity,
as if plant-humankind.
if that not, dream may be another brain activity.
however, sleeping dream can't be the normal activity of human brain.
because sleeping-night was the rest time of brain-activity.
so, dream could be a good or bad omen accroding to each dream -analyzers.
at any rate, only sleeping-dream is arbitary by dream-interpreter.
by that sense, dream could be wish or fear-sleeping to humankind.

sun admitted day to man
mood also night to woman
by harmony of sun and moon
day and night will be born
on night, go to sleep and dream
after next morning
dream comes true best or worst

Animals dream as well. Probably simply because some parts of the brain and body remain active- the parts that we don't have conscious control over. Sort of like a computer that you use to do various tasks during the day that has to stay active after you're no longer using it processing what you've entered and maintaining itself. The dreams are part of the maintenance process that we barely have any understanding of.

Sleep

There are a lot of theories, but it seems to be the mind moving memories from short term storage to long term.

“I dream my painting and I paint my dream.”
― Vincent Van Gogh

We still don't know why we sleep.