Ingersoll was most noted as an orator, the most popular of the age, when oratory was public entertainment. He spoke on every subject, from Shakespeare to Reconstruction, but his most popular subjects were agnosticism and the sanctity and refuge of the family. He committed his speeches to memory although they were sometimes more than three hours long. His audiences were said never to be restless.
His radical views on religion, slavery, woman's suffrage, and other issues of the day effectively prevented him from ever pursuing or holding political offices higher than that of state attorney general. Illinois Republicans tried to pressure him into running for governor on the condition that Ingersoll conceal his agnosticism during the campaign, which he refused on the basis that concealing information from the public was immoral.
Many of Ingersoll's speeches advocated freethought and humanism, and often poked fun at religious belief. For this the press often attacked him, but neither his views nor the negative press could stop his rising popularity. At the height of Ingersoll's fame, audiences would pay $1 or more to hear him speak, a giant sum for his day.
Source: quotes from Wikipedia