On the occasion of the fourth centenary of the birth of Blaise Pascal (19-06-1623 - 19-08-1662), Pope Francis wrote this Apostolic Letter. The goal is that his work may enlighten us and the example of his life immersed in Christ may help us on the path of truth, conversion and charity. His basic attitude was "astonished openness to reality". He explored the human condition and the paradox is at the heart of his message: the greatness and misery of man. He was a brilliant thinker and sensitive to the needs of the poor. In the last days of his life - he died when he was only 39 years old - he had the urgency to dedicate himself to the works of mercy. The reading of this pontifical document can help us to seek true happiness with reason and with the heart.