That is the title of a book I have read over Lent that has truly changed my life. Written by a priest, Michael Gaitley, it is based on the teachings of St. Therese of Lisieux and St. Faustina. It teaches all about prayer, about having a trusting relationship with Jesus, what he really wants from us, and how to give that to him, in a way that is clear, easy to understand, and not overwhelming. It has changed my life. I can't recommend this book enough.