Books on Amazon:
Religion/Ethics/P. Singer: Thesis: Ethics is not only accessible in the context of a religion. It is even completely independent of religion. (> Euthyphron: "Good is what pleases the gods.").
P. SingerVsEuthyphro: the argument boils down to a circularity: in the end, God is good because he pleases God. ((s) > Euthyphro/Geach).
Ethics/Kant/P. Singer: Kant rejected any self-interest in the observance of ethical rules (for example, the avoidance of agony) and demanded that the laws should be obeyed for the sake of themselves.
Religion/Ethics/P. Singer: Thesis: our daily observation shows that ethical behavior does not require belief in heaven and hell, and vice versa, such a belief does not always lead to ethical behavior.
Practical Ethics (Third Edition) Cambridge 2011
The Most Good You Can Do: How Effective Altruism is Changing Ideas About Living Ethically. New Haven 2015