what is the purpose of our dreams when we went to sleep on earth?
Each person is different. So, there can be a different purpose for each person's dreams. And every dream could have a different purpose . . . good or bad, depending on who brings the dream.
But a lot of dreams might not have purposes which are personal, but . . . in my opinion . . . in general dreams might have a practical physiological purpose >
During sleep people have a very high level of brain activity. And what becomes of you after some nice sleep? You are more clear; not only are you rested but you and do things better . . . more efficiently.
Sleep is very active; yet, it does not make you tired! How can this be?
I think it is because your brain cleans itself out during the sleep process, so it can do things more efficiently.
It is like how you can have a very busy day at work, so your desktop is cluttered with unopened mail and torn-open envelopes and messages. So, you need to clear that waste stuff away but preserve and put in order any mail and messages which are still needed; or else your next day will start off already mixed up.
Like this, your brain's nerves have chemical mail used to pass messages from one nerve to another. After a day of this, there is all the chemical stuff left over, built-up. It needs to be removed so your nerves have clear ways to pass their messages on to other nerves, without leftover chemicals mixing with it and slowing things down. And your brain stores things from the messages and experiences of the previous day, but not right in the midst of the next day's active messaging of the nerves.
So, rest is not all you need, at the end of the day.
And my opinion is that dreams could have a very basic function > to test your brain function to see how well it has been cleared out. Then your brain goes on to do more clearing, then another test dream
But there can be dreams which are God personally sharing with you. In your sleep during dreams, I suspect we are acting in our true character, maybe more than while awake; and so by reaching us in a dream during sleep, God could be communicating the most personally possible with us more the way we really are . . . while all our defenses are inactive and we are not busy pushing to make things happen.
So, when I wake up and I know I wasn't being spiritual and kind and about God during a dream, I can be worried and praying for God to really change my character to be like Jesus so I am not the way I can be otherwise.
And there can be Satanic and worldly dreams, which we can give in to, or we can defeat.
A dream which is from God will have God's purpose, of course; but even a bad dream can be turned to good use, right? . . . yes, with God