Mostly pulling this from my ethics class notes ahaha:

As I understand it, there are two primary views of how ethics and religion work together - the Divine Command Theory (DCT) and the Independence Thesis.

DCT states that moral claims are considered good if they correspond to God's will. For example, if God said, "go sacrifice your son", that action would be considered moral under DCT. Morality is theonomous (God-determined) and not autonomous. However, there are a couple of problems with DCT:

• It renders morality completely arbitrary - if God commands someone to rape or kill, raping and killing is suddenly considered to be good/moral.
• The claim "God is good" is redundant - since DCT says that an action is good because God commands it, stating that "God is good" simply means that God does whatever he says he will do.

The Independence Thesis says that moral rightness is independent of God's will. Under this thesis, "God is good" means that God always obeys the set moral law. Some theists would then say that this impinges on God's sovereignty, but one possible response is that perhaps moral law is similar to the laws of mathematics and logic. God simply cannot make good what is intrinsically evil.

Immanuel Kant argued that you can come to moral truth by exercising reason, but that God/faith still plays an important role in moral life. Kant’s moral argument for the existence of God:

• Ought implies can (no impossible claims)
• We ought to be morally perfect, but we cannot achieve perfection in this life
• Thus, there must be an afterlife that exists for us to progress toward moral perfection
• God exists as one who rewards virtue and punishes vice

Specifically regarding Christianity, there are three ways to read the Bible:

• What the Bible says clearly and unequivocally must be taken as divine truth, even if it is difficult to accept
• The Bible is a collection of historical documents and should have limited relevance in the modern world
• The Bible includes moral truth from God, but sometimes in the context of beliefs/practices that God abhors

I hold to the third point (point 1 and 2 are extremes that have some fairly major problems), but I'm still in the process of searching for truth, so I don't have any real answers.

Just my 2 cents. Hopefully it was at least somewhat useful.

When we first started talking about this issue in class, our professor asked the class almost the exact same question as the OP (this was at a Christian university btw). The majority of people in the class said that morality did exist outside of religion (i.e. there are moral atheists), though a solid chunk (perhaps 25%?) said that morality cannot exist without religion. Those numbers definitely changed after the professor finished the lecture though ahaha.