The dialectical opposition and interaction of the secular and the spiritual realms of life has deep roots in Christian thought. Jesus enjoined his challengers to “render unto Caesar the things which are Caesar's and unto God the things that are God's” (Matt 22:21). To his disciples he said, “That which is born of the flesh is flesh, and that which is born of the Spirit is spirit” (John 3:6), and “except a man be born of … the Spirit, he cannot enter the kingdom of God.” (John 3:5).
St. Paul, in turn, contrasted “the inward man,” who delights in “the law of God,” with one who is “in the flesh,” the law of whose “members” wars against “the law of the spirit” (Rom 7:5-7, 22-23). He listed among the “spiritual gifts” implanted by God in followers of Christ the gifts of wisdom, of knowledge, of faith, of healing, of miracles, and of prophecy (1 Cor 12:1-7). The spiritually minded inner-directed follower of Christ fights against the materialism of the unredeemed age, the time-bound world, into which he was born.
Four centuries later St. Augustine applied this concept to the society in which he lived, drawing a sharp contrast between the sinful and, indeed, Satanic character of the temporal “earthly city” and the purity of the eternal “city of God.” For St. Augustine, both the church and the empire lived in an evil age, in hoc maligno saeculo, in which the true Christian, whether priest or layman, was, in effect, an alien. In Peter Brown's words, “For Augustine, this saeculum is a profoundly sinister thing. It is a penal existence … it wobbles up and down without rhyme or reason.” In the City of God, on the other hand, Christian spirituality, for St. Augustine, was effectuated through the “vestiges” of the tri-une God implanted in human memory and imagination, human reason and understanding, and human desire and love.