In Pilgrim Letters, Curtis Freeman takes disciples on a contemporary journey into an ancient faith. The book is a series of letters written by "Interpreter" to "Pilgrim" that provide "instruction in the basic teaching of Christ" for candidates preparing to be baptized. The letters are framed by a short catechism based on the six principles enumerated in Hebrews 6:1-2—(1) repentance, (2) faith, (3) baptism, (4) laying on of hands, (5) resurrection, and (6) eternal judgment.

The letters lead Pilgrim (the disciple/catechumen/baptismal candidate) step by step through the basics of Christian faith. Each letter explores one of the principles by providing a simple explanation and setting the practice within a broad biblical, historical, and theological context. The theological tenor of the letters is evangelical-catholic, free church-ecumenical, and ancient-future. A set of discussion questions follows each letter as does a short bibliography for further reading. Each letter begins with an image from William Blake's illustrations of John Bunyan's The Pilgrim's Progress and exemplifying the subject of the letter, followed by an epigraph from the story that fits into the themes of the catechism.