To explain Cursillo to someone who has not experienced Cursillo is, at best, difficult. It’s not because Cursillo is a secret, but because it is a living experience that one must experience firsthand. No one can fully explain how God touches a person. Christ, through the Cursillo and through His grace, touches the person who is open to a personal relationship with Him in a special way.
The Cursillo can help the person in developing a deeper understanding of what it means to be fully Catholic by being fully Christian in order to exercise their mission as baptized individuals.
The world [in the mid 20th Century] was in chaos because baptized men were not aware of the potential that the Grace of God gives them to be and live as Christians. Cursillo put its emphasis on being Christian, not on doing Christian things; it opted for an apostolic movement based on the associated strength of friendship.