Against Celsus (Greek: Κατὰ Κέλσου; Latin: Contra Celsum), preserved entirely in Greek, was Origen's last treatise, written about 248.
It is an apologetic work defending orthodox Christianity against the attacks of the pagan philosopher Celsus, who was seen in the ancient world as early Christianity's foremost opponent.
In 178, Celsus had written a polemic entitled On the True Word, in which he had made numerous arguments against Christianity.
The church had responded by ignoring Celsus's attacks, but Origen's patron Ambrose brought the matter to his attention.
Origen initially wanted to ignore Celsus and let his attacks fade, but one of Celsus's major claims, which held that no self-respecting philosopher of the Platonic tradition would ever be so stupid as to become a Christian, provoked him to write a rebuttal.

In the book, Origen systematically refutes each of Celsus' arguments point-by-point and argues for a rational basis of Christian faith.
Origen draws heavily on the teachings of Plato and argues that Christianity and Greek philosophy are not incompatible, and that philosophy contains much that is true and admirable, but that the Bible contains far greater wisdom than anything Greek philosophers could ever grasp.
Origen responds to Celsus's accusation that Jesus had performed his miracles using magic rather than divine powers by asserting that, unlike magicians, Jesus had not performed his miracles for show, but rather to reform his audiences.
Contra Celsum became the most influential of all early Christian apologetics works; before it was written, Christianity was seen by many as merely a folk religion for the illiterate and uneducated, but Origen raised it to a level of academic respectability.
Eusebius admired Against Celsus so much that, in his Against Hierocles 1, he declared that Against Celsus provided an adequate rebuttal to all criticisms the church would ever face.
Against Celsus (Greek: Κατὰ Κέλσου; Latin: Contra Celsum), preserved entirely in Greek, was Origen's last treatise, written about 248. It is an apologetic work defending orthodox Christianity against the attacks of the pagan philosopher Celsus, who was seen in the ancient world as early Christianity's foremost opponent. In 178, Celsus had written a polemic entitled On the True Word, in which he had made numerous arguments against Christianity. The church had responded by ignoring Celsus's attacks, but Origen's patron Ambrose brought the matter to his attention. Origen initially wanted to ignore Celsus and let his attacks fade, but one of Celsus's major claims, which held that no self-respecting philosopher of the Platonic tradition would ever be so stupid as to become a Christian, provoked him to write a rebuttal.
In the book, Origen systematically refutes each of Celsus' arguments point-by-point and argues for a rational basis of Christian faith. Origen draws heavily on the teachings of Plato and argues that Christianity and Greek philosophy are not incompatible, and that philosophy contains much that is true and admirable, but that the Bible contains far greater wisdom than anything Greek philosophers could ever grasp. Origen responds to Celsus's accusation that Jesus had performed his miracles using magic rather than divine powers by asserting that, unlike magicians, Jesus had not performed his miracles for show, but rather to reform his audiences. Contra Celsum became the most influential of all early Christian apologetics works; before it was written, Christianity was seen by many as merely a folk religion for the illiterate and uneducated, but Origen raised it to a level of academic respectability. Eusebius admired Against Celsus so much that, in his Against Hierocles 1, he declared that Against Celsus provided an adequate rebuttal to all criticisms the church would ever face.
Origen