I’d like to know, what do humans and angels have in common?
Both humans and angels are creatures of God. They are both persons with spiritual souls and thus created to be immortal. The main difference between humans and angels is that humans have bodies and angels don’t. Because angels do not have bodies that subject them to time and change, they have superior intellects and their choices are eternal. That is why the fallen angels could not be redeemed: Their choice to reject God was permanent and could not change. Those angels who chose God also chose permanently and now cannot fall.