A place made for one to sit and belong. In a council, a seat is a standing to speak that persists between meetings.
Old Norse saeti (a seat, a place to sit), from Proto-Germanic *setiz, related to sit; in a council, the seat has always meant a standing to speak, not merely a place to rest.
A place made to sit and belong, and in a council, a standing to speak that outlasts any single meeting held in it.