Why would Satan want souls? What use are they to him?

[Tonus]

Then...why do "we" exist? Why does anything exist?

What you are saying is there is no [reason] for life, except to die. And that there was no basis we are brought into being.

This may be the most dangerous part of religion, in my mind. The idea that life has some kind of greater meaning that can only be fully attained after our life is over. It gives people a reason to live a simple and complacent life regardless of circumstances and to avoid ambition or the motivation to constantly improve themselves and their lifestyle. Far too many people give up on the only life they'll ever have because they think there's a much greater life that will begin when they die. That's tragic, IMO.

To a logical person, that should make no sense at all. There is always a reason (cause & effect)....some reasons we aren't sure of. So we search.

There is no reason why it should be logical to expect there to be some greater, overarching meaning to the existence of the universe, or of Earth, or of humanity. As we search for the "how" of the universe it is possible we will uncover a "why." But making up a "why" because we don't understand the "how" is not a way to make progress, it's just a shortcut, and it can be an obstacle towards a better understanding of our world and universe.