Starting in 1928, Marc Boegner gave yearly Lenten addresses, on various religious and theological themes, in his parish of Passy (Paris). These addresses, which were broadcast live on French radio and subsequently published as books, shed light on how one of the pillars of Reformed Protestantism in France thought about Christianity in the modern world. An analysis of these texts reveals a strong apologetic intention as well as a courageous ecumenical outlook, at a time when dialogue with Roman Catholics and Eastern Orthodoxy was still in its infancy. The influence of Boegner’s uncle Tommy Fallot, as well as of Father Laberthonnière, is evident throughout, notably in his warnings his listeners and readers not to fall prey to the totalitarian ideologies of the day (i.e., communism, fascism), to resist all forms of idolatry, and to embody the ‘solidarities God asks of us.’