Bill Potter at Landmark Events.
"Why did a descendant of rabbis on both sides of his family, for generations, suddenly enter the Lutheran Church? Marx’s father enjoyed a successful law practice in the city of Trier along the Moselle River. Although he knew Voltaire and other radical skeptics by heart, when the Prussian government imposed the requirement of belonging to the state church in order to practice law, Heinrich agreed to baptism for himself and his children."
See Marx, Capital, and Marx and Engels, Manifesto of the Communist Party, Great Books of the Western World (first edition, 52 Vol., 1952) volume 50, (second edition, 60 Vol., 1990) volume 50.