Living the Sermon on the Mount in difficult times is part of what it means to follow Jesus, the Peaceful One. Jesus not only taught it, he lived it. This introduction, for all kinds of Christians, examines the revolutionary content of Jesus' Sermon on the Mount in the context of the brutal Roman empire. Then it surveys stories of those who struggled to faithfully live this Scripture in the messiness of their own difficult times. What does this history look like from perspective of the cross? Violence served Roman, European and American empires well, but crucified their victims. This text seeks to feminize and decolonize the debate as to whether the Sermon on the Mount is relevant today, then ask how relevant the just war tradition and Christian realism are for addressing the big human security questions of the twenty-first century: climate change, poverty, mass migration, racism, populism, and nuclear weapons. Learning from the past, can we begin to develop a new, robust Christian realism, that takes seriously the Sermon on the Mount and finds in it a way of salvation for our own difficult, poly-crisis times? This book can be read individually and also as a group study.