Augustine of Hippo — as excerpted in the Catena Aurea on Mark 16:19-20

“(Epist. cxcix. 12.) (Acts 1:8) But how was this preaching fulfilled by the Apostles, since there are many nations in which it has just begun, and others in which it has not yet begun to be fulfilled? Truly then this precept was not so laid upon the Apostles by our Lord, as though they alone to whom He then spoke were to fulfil so great a charge; in the same way as He says, Behold, I am with you always, even unto the end of the world, apparently to them alone; but who does not understand that the promise is made to the Catholic Church, which though some are dying, others are born, shall be here unto the end of the world?”