This is the third in the series of letters Marx [age 25] wrote to his friend, Arnold Ruge, during 1843 – it is also the last in the eight letter exchange. Marx and Ruge would include the entire series in the first and only edition of their joint venture, the Deutsch-Franzosische Jahrbucher, February 1844.
Marx is replying to Ruge's previous letter, in which Ruge proclaimed himself an atheist and a vigorous supporter of the "new philosophers". (Description Source: Marx Engels Internet Archive)