The Gospel of Buddha is a compilation rather than a single ancient text. Paul Carus gathered passages from the Buddhist canon and related sources and arranged them, with some rearranging and abbreviation, into one continuous story of the Buddha's life and teaching. He frames it deliberately as a gospel, with introductory and concluding chapters of his own and a table of references for readers who want to trace each part to its origin.
The introduction lays out the doctrine before the narrative begins. Everything in the world is transient; this is Samsara. Yet within the changes there is a constancy of law, and where the law is seen there is truth. Carus draws a sharp line between self and truth: self is the cause of selfishness and the germ of evil, while truth cleaves to no self and leads to righteousness. The extinction of self is presented as salvation and as the meaning of Nirvana.
The life of Siddhattha follows. Sheltered from all suffering in his father's palace, the prince rides out and meets old age, sickness, and death, the three woes that shatter his ease. He renounces his home, tries severe self-mortification, abandons it as useless, and at last attains enlightenment under the bodhi tree after facing Mara the tempter. At Benares he preaches his first sermon, setting out the middle path, the four noble truths, and the eightfold path, and sets the wheel of the law rolling.
Much of the book then records the building of the community and the teaching itself. Disciples are gathered, the Sangha and its rules take shape, and the Buddha answers questions on identity, Nirvana, and conduct. A long section of parables and stories carries the doctrine into ordinary life: the mustard seed that teaches a grieving mother that death is common to all, the lost son, the widow's mites, the outcast, and others that meet sorrow, pride, and cruelty with patience and insight.
The closing chapters describe the last days, the final entering into Nirvana, and the Buddha's parting charge to work out salvation with diligence and to treat the law itself as teacher once he is gone. Carus's own conclusion gathers the whole into a single theme: truth has no room to dwell in mere space or sentiency or reason, but finds its home in the righteous human heart. That, in his arrangement, is the purpose of being and the gospel of the Blessed One.