Although she was just a humble young woman from a small town, Mary's total "yes" to God was "the most important 'yes' of history" and overturned Adam and Eve's prideful "no", which unleashed sin into the world, Pope Francis has said.

"With generosity and trust like Mary, may each of us say this personal 'yes' to God today," Pope Francis prayed as he recited the Angelus prayer with visitors in St Peter's Square on the feast of the Immaculate Conception.

Even when they do not say "no" to God, human beings can be experts in saying, "yes, but ..." to God, the Pope said.