Isaiah 22:21-22:
“… and I will clothe him with your robe, and will bind your girdle on him, and will commit your authority to his hand; and he shall be a father to the inhabitants of Jerusalem and to the house of Judah. And I will place on his shoulder the key of the house of David; he shall open and none shall shut, and he shall shut and none shall open.”
Corresponds with Matthew 16:18-19:
“And I tell you, you are Peter and on this rock I will build my church, and the powers of death shall not prevail against it. I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.”
The key represents the office of prime minister.