unity[574] as in the case of Christ, viewed as the second Adam. The teachings in III. 21. 10-23[575] show what an almost naturalistic shape the religious quasi-historical idea assumed in Irenaeus' mind. This is, however, more especially evident from the assertion, in opposition to Tatian, that unless Adam himself had been saved by Christ, God would have been overcome by the devil.[576] It was merely his moralistic train of thought that saved him from the conclusion that there is a restoration of _all_ individual men. This conception of Adam as the representative of humanity corresponds to Irenaeus' doctrine of the God-man. The historical importance of this author lies in the development of the Christology. At the present day, ecclesiastical Christianity, so far as it seriously believes in the unity of the divine and human in Jesus Christ and deduces the divine manhood from the work of Christ as his deification, still occupies the same standpoint as Irenaeus did. Tertullian by no means matched him here; he too has the formula in a few passages, but he cannot, like Irenaeus, account for its content. On the other hand we owe to him the idea of the "two natures," which remain in their integrity--that formula which owes its adoption to the influence of Leo I. and at bottom contradicts Irenaeus' thought "the Son of God became the Son of man," ("filius dei factus filius hominis"). Finally, the manner in which Irenaeus tried to interpret the historical utterances about Jesus Christ from the standpoint of the Divine manhood idea, and to give them a significance in regard to salvation is also an epoch-making fact.