"The keys of the kingdom"
From the beginning of his public life Jesus chose certain men, twelve in number, to be with him and to participate in his mission. He gives the Twelve a share in his authority and 'sent them out to preach the kingdom of God and to heal." They remain associated for ever with Christ's kingdom, for through them he directs the Church:
As my Father appointed a kingdom for me, so do I appoint for you that you may eat and drink at my table in my kingdom, and sit on thrones judging the twelve tribes of Israel.
Source: Catechism of the Catholic Church (Vatican.va)