Christian books that explain Christian spirituality in practical terms, targeting fence-sitter agnostics looking for clarity?

Are there Christian books for fence-sitter agnostics—those for whom spirituality and God feel as foreign as trying to explain colors to someone blind from birth or quantum mechanics to a 5-year-old? Such readers might be curious about what Christian spirituality actually entails: what it means, in practical terms, to have a "relationship" with an unseen, undetectable being who, if real, seems hidden in another dimension. How is this relationship supposed to work? How might such a being interact with you? Are there books that address these questions directly, making Christian spirituality concrete and relatable instead of abstract and vague? Ideally, these books would use down-to-earth examples and clear language, leaving readers with genuine insights instead of confusion. Additionally, the book should explore what readers might expect if they choose to engage more deeply in Christian spirituality. What does it mean to "go deep" in a spiritual context? What kinds of experiences or changes—emotional, mental, spiritual, or even supernatural—might they encounter? Clear explanations of this deepening process, with illustrative examples of what a genuine journey of faith might look like, would provide the reader with a clearer roadmap to understanding. Regarding denominations, I'm open to multiple perspectives, so it would be great to receive book recommendations representing the major branches of Christianity—namely, Catholicism, Orthodoxy, and the major subbranches of Protestantism, including Evangelicalism, Anglicanism, Lutheranism, and Pentecostalism/Charismatic traditions. This way, I can gain a well-rounded understanding of Christian spirituality as viewed through different theological lenses, practices, and traditions.