Rewards

In the end, and despite a long history of schism and controversy concerning soteriology, Christianity turns on its promise of salvation: the reward of eternal life.
What happens to ethical thought when this doctrine of reward in the afterlife lose its credibility?
We can then secularize reward: utilitarianism proposes a this-worldly reward-based schema, as do all those politico-ethical programs which call upon a notion of historical progress (e.g. marxism). All of these share the structure of Christian thought. (That's true, however much I dislike the implications of this thought.)
Or we can jettison reward. For the most part this means that sanctioned end-directed activity must be performed for its own sake (i.e. Kantianism) or for ends which cannot be construed as rewards, usually because they are merely expressive, that is, they express something of value.
Two particular such expressive ethics have had wide circulation: one based on authenticity (Heidegger), the other based on style (Nietzsche).
The first of these, the turn to authenticity, tends towards nostalgia, deploring historical fragmentation or loss (a nostalgia which is also embedded in Christianity of course).
And so: within this array, Nietzsche offers the most stringently secular way.