A commented gospel, not a new gospel
When Allan Kardec wrote this book, in 1864, he had already begun the codification of Spiritist doctrine with an earlier title. Here the approach changes: instead of organizing questions and answers about the beyond, he takes the four Gospels and pulls out only the moral passages of Jesus, leaving aside miracles and passages that, in his view, demand too much blind faith from someone who wants to think with reason. The result is not a new gospel, it's a commented reading of what already existed.
The audience the book says it aims at is also striking: it isn't written to convert people who believe in nothing, but for those who already consider themselves Christian and want to understand the morals of the Gospels without contradicting reason, or for those who already follow Spiritist doctrine and want an ecumenical reading that speaks to the Christianity they learned at home.
It's like the person who goes to Mass on Sundays and, during the week, reads a spirituality book trying to join the faith inherited from the family with an explanation that makes sense to a modern mind. The book sets out to build exactly that bridge, without asking anyone to leave the church they attend.
