This is for those Angel people. Angels are among the unseen in the "all that is, seen and unseen" that the Nicene Creed says the Father created.
They don't decay or die, since they are spiritual beings. They exist to praise God and to bear the message and task for which God sends them, including to us humans. They can think and hold conversations, and they have their own identity.
And they appear to people of all religions, even those of no religion at all, when God wants them to listen. Noone can prove angels exist; they are, after all, spiritual beings and don't fit into material-world rules. But those who have a strong sense of spirituality tend to believe angels are real, and sometimes experience their presence.