After his victory at the Milvian Bridge, faithful to his promise, Constantine favors the church from which he has received support. Catholic Christianity becomes the state religion and an exchange takes place: the church is invested with political power, and it invests the emperor with religious power. ... The church lets itself be seduced, invaded, dominated by the ease with which it can now spread the gospel by force (another force than that of God) and use its influence to make the state, too, Christian. It is great acquiescence to the temptation Jesus himself resisted, for when Satan offers to give him all the kingdoms of the earth, Jesus refuses, but the church accepts.
Jacques Ellul, The Subversion of Christianity (1982), G. Bromiley, trans. (1986), p. 124