(a) Incarnational investment in “nature”
Taylor’s case-in-point w/r/t his "zig-zag" approach is a shift to a new interest in “nature,” or more specifically nature “for its own sake” (90). Now, from the vantage of point of secular humanism, this new interest in nature can look like the next logical step on the way to pure immanence: first distinguish God/nature, then disenchant, then be happy and content with just nature and hence affirm the autonomy and sufficiency of nature. Such a story about the “autonomization” of nature posits a contrast or dichotomy between belief in God and interest in “nature-for-itself” (91).
The only problem with such a story is that it fails to account for two important historical realities: (1) it was precisely Christians who were exhibiting a new interest in creation/nature for theological reasons; and (2) this interest was clearly not mutually exclusive with belief in God and an affirmation of transcendence. In particular, the late medieval and Renaissance investment in nature/embodiment/particularity is rooted in a new Incarnational spirituality (93ff.). This was very much an “evangelical” development, concerned with bringing Christ to the world, and thus recognizing God’s own “incarnational” move in that regard—meeting humanity where it is, in bodies, history, etc. “So it is not altogether surprising that this attempt to bring Christ to the world, the lay world, the previously unhallowed world, should inspire a new focus on this world” (94). This can be seen in art during this period as well (96). So this was primarily a revolution in devotion, not metaphysics. Thus “the new interest in nature was not a step outside of a religious outlook, even partially; it was a mutation [?] within this outlook” (95). While this shift might, from a later vantage point, look like the first step toward exclusive humanism and pure immanence, it was not at the beginning—and could have gone otherwise.
(b) Complications: the nominalist revolution
True to his zig-zag account of causal complexity, Taylor notes another development, roughly parallel to the incarnational emphasis: the rise of nominalism which is a metaphysical thesis. Now, Taylor notes that nominalism was not a proto-secularism precisely because the motives behind nominalism were fundamentally theological. In particular, nominalism arose as a way of metaphysically honoring a radical sense of God’s sovereignty and power. The issue is this: Aristotelian notions of a human “nature” saw the good of the human being determined by the nature or telos of the human being: so there was a defined way to be good. Now while God the Creator might have created this telos or nature, once created it would seem to actually put a constraint on God, since enabling humans to achieve their (good) end would require that God sort of “conform” to this good/telos.
“But this seemed to some thinkers an unacceptable attempt to limit God’s sovereignty. God must always remain free to determine what is good” (97). DISCUSS. So if one was going to preserve God’s absolute sovereignty, one would have to do away with “essences,” with independent “natures.” And the result is a metaphysical picture called “nominalism” where things are only what they are named (nom-ed, 97).
“But if this is right,” Taylor comments, “then we, the dependent, created agents, have also to relate to things not in terms of the normative patterns they reveal, but in terms of the autonomous super-purposes of our creator [which can’t be known a priori]. The purposes things serve are extrinsic to them. They stance is fundamentally one of instrumental reason” (97). Part of the fall-out of such a metaphysical shift is the loss of final causality, the eclipsing of any teleology for things/nature. Understanding something is no longer a matter of understanding its “essence” and hence telos; rather, it requires a “mechanistic” concern with efficient causality that can only be discerned by empirical observation: hence, the scientific method, etc. The result is nothing short of “a new understanding of being, according to which, all intrinsic purposes having been expelled, final causation drops out, and efficient causation alone remains” (98).
But keep in mind Taylor’s zig-zag point: the incarnational interest in nature was not necessarily a step on the way to the autonomization of nature; rather, only when it is “mixed” with another development, nominalism, does it seem to head in that direction. But it could have been otherwise, and without the triumph of nominalism we might have had a very different concern with nature for its own sake.
 [It is fascinating (at least to me) to consider how much such a story informed Francis Schaefer’s “big story” about the West. But Schaefer saw the Frankensteinish catalyst for this in Aquinas’ distinction between nature and grace and then tended to see the Reformers as resisting this; whereas Taylor sees Aquinas’ working with still a fundamentally “enchanted” ontology and sees the real shift in the Reformers.]
 Recall Ruskin’s “two Renaissances.”