How does Marshall know so much about Mormonism? His passion to know if Mormonism is true drove him to collect as many original books on Mormonism, from the 1800s as he could find. This is how he is able to "know" if Mormonism is true or not and reach out to others with the truth that religion is not what saves, but trusting in Jesus alone is the only way to be saved (John 4:12).