Then we wouldn’t have difficult answers like this. We wouldn’t hear that the next pope needs to make secularism the centerpiece of his agenda, and we wouldn’t fault Islam for failing to distinguish between religious and secular authority. Instead, we would fault Christians for similarly failing to own up to the secular nature of the period between the advents of Christ, also known as saeculum (or age), when the old kingdom of God’s people is no longer the political arrangement and the new Jerusalem has yet to come, the one where Christians are pilgrims and strangers, and where the don’t identify the kingdom of grace with the monarch’s kingdom.
Why doesn’t anyone read not C.S. but Bernard Lewis?
Secularism in the modern political meaning – the idea that religion and political authority, church and state are different, and can or should be separated – is, in a profound sense, Christian. Its origins may be traced in the teaching of Christ, confirmed by the experience of the first Christians; its later development was shaped and, in a sense, imposed by the subsequent history of Christendom. The persecutions endured by the early church made it clear that a separation between the two was possible; the persecutions inflicted by later churches persuaded many Christians that such a separation was necessary.
The older religions of mankind were all related to – were in a sense a part of – authority, whether of the tribe, the city, or the king. The cult provided a visible symbol of group identity and loyalty; the faith provided sanction for the ruler and his laws. Something of this pre-Christian function of religion survives, or reappears, in Christendom, where from time to time priests exercised temporal power, and kings claimed divine right even over the church. But these were aberrations from Christian norms, seen and reciprocally denounced as such by royal and clerical spokesmen. The authoritative Christian text on these matters is the famous passage in Matthew 22:21, in which Christ is quoted as saying, “render therefore unto Caesar the things which are Caesar’s; and unto God the things that are God’s.” Commentators have differed as to the precise meaning and intention of this phrase, but for most of Christian history it has been understood as authorizing the separate coexistence of two authorities, the one charged with matters of religion, the other with what we would nowadays call politics.
In this, the practice of Christianity was in marked contrast with both its precursors and its competitors. In imperial Rome Caesar was God, reasserting a doctrine that goes back to the god-kings of remote antiquity. Among the Jews, for whose beliefs Josephus coined the term “theocracy,” God was Caesar. For the Muslims, too, God was the supreme sovereign, and the caliph was his vice-gerent, “his shadow on earth.” Only in Christendom did God and Caesar coexist in the state, albeit with considerable development, variety, and sometimes conflict in the relations between them. (What Went Wrong? Western Impact and Middle Eastern Response, 2002, 96-97)