The one who sits at the gate in the Old Testament is the one who judges or mediates over the daily disputes/affairs of the people. Just like Moses in Exodus 18:13-16.

13 On the next day, Moses sat to judge the people, and the people stood around Moses from the morning until the evening. 14 When Moses’ father-in-law saw all that he was doing for the people, he said, “What is this thing that you are doing for the people? Why are you sitting by yourself while all the people stand around you from morning until evening?”

15 Then Moses said to his father-in-law, “Because the people come to me to inquire of God. 16 When they have a dispute, it comes to me, and I judge between a man and his neighbor, and I make known the statutes of God and His laws.”