http://history-and-evolution.com/whee4th/intro1_2_4.htm: The rise of the modern, pace the ‘eonic effect’
Discussions of ‘secularism’ never go anywhere, but a look at the ‘eonic effect’ and also the latin ‘saeculum’ for ‘age period’ (or something like that, Wikipedia has a different take, i think this correct for seventeenth century semantics) might help: the rise of the modern there is seen via a ‘finite transition model’ i.e. the modern ‘transition’ from 1500 to 1800, a highly useful if slightly arbitrary feature of the model. The term ‘secular’ deserves a good scholarly history but seems to have come into existence in roughly the same way as ‘medieval’ from ‘medium aevum’ when people began to sense the great take off, first with the Reformation, then especially in the seventeenth century (the first taste of the ‘enlightenment’). The secular is a ‘change in age period’ or the new epoch or ‘new age’ of modernity, with a broad spectrum of content, religious and anti-religious.
The confusion can be seen by backtracking to the Axial Age, and its earlier ‘new saeculum’, which attacked earlier traditions of religion in the name of a new ‘secular’ or epochal religion formation. Note the irony here. To be sure, in classical Axial Greece the ‘secular’ in a post-religious sense begins to emerge, but even there the form of aesthetic polytheism (witness the Parthenon) shows just as much ‘religion’ as Israel, arguably.
The modern ‘secular’ is confusing because religious transformation, and the passing of Axial religion is confused with atheism and anti-religion. But, pace the New Age movement, religion is exploding, but in ways still unformulated for a new future. Atheism remains a perfectly good ‘secular’ option, but its forms tend to be so shallow that religion always jumpstarts into a new comeback.