John Baillie was a Scottish theologian and author, born in 1886 and known for his contributions to Christian thought. He served as a professor at Union Theological Seminary in New York City and was influential in the development of modern theology. His works often focused on the relationship between faith and experience. Baillie is perhaps best known for his book, A Diary of Private Prayer, which has been widely used for personal devotion. He emphasized the importance of prayer and spiritual reflection in everyday life, making his writings accessible to both scholars and laypeople alike.