All the great works of classical literature that we can enjoy today survive only because throughout the middle ages Christian monks laboriously copied them out in their scriptoria. The Latin language itself is likewise an ancestral treasure. It's a gift from our distant ancestors that the Church has kept safe for us over two millennia.
The Weightiest of Reasons: The Pope and Latin in the Liturgy
Contrary to the common misconception, however, the council did not retire the Latin language. Furthermore, as the quote above demonstrates, John XXIII would have strenuously opposed any attempts to do so. In any case, the council and the pope were in agreement.