[From Pensieri su Paulo, by Pope Benedict XVI]
"St. Paul was tirelessly on the journey, bearing with himself the Gospel. He felt himself absolutely under a sort of "compulsion" to announce the Gospel (1 Cor 9:16) -- not so much because of a preoccupation for the salvation of any individual non-baptized person, not yet joined to the Gospel, but because he was aware that the whole history could not arrive at its fulfillment until the totality (pléroma) of the people were not joined to the Gospel (cf. Rom 11:25)."
(From his Discourse to the Roman Curia, Dec. 21, 2007. Def. worth reading in its entirety. You'll also get, quite likely, a more precise translation of this excerpt there. :))