Religion is not necessary for morality

Here, Kant says that unless you would wish your maxim (the motivating principle) of your action to become a universal law, you should never act in such a way. This is then easily proven by means of imagining a situation where a person's circumstances can be improved by making a promise known to be impossible to keep. While it certainly might bring about some amount of alleviation in the short term, it is by no means something one could wish to become universal. That is because in a world where nobody keeps their promises, the whole concept of promise is undermined, and therefore the morality of such an action does not hold. This shows how pure reasoning can be used to arrive at a scalable moral principle that can be universally applied while not requiring an external command or supervision to encourage a moral act.

2. Mutual benefit principle

This is a simple but powerful concept, often mentioned by thinkers like Matt Dillahunty, that arrives in a similar place as the first argument and can be best described as follows: If I behave in a socially acceptable manner (not stealing from, taking advantage of, harming or neglecting others), by doing that I will therefore encourage other people to do so and thus being moral and thoughtful of others becomes something everyone is interested in. Here, the focus is on thinking how I would wish others to treat me and then acting in the same way. If I don't want to be stolen from, I shouldn't steal myself and encourage punishment for those who do steal. If I do not wish to be lied to, I shouldn't lie. Thus, this principle, even if all action is based solely on personal interest, provides a sustainable moral framework, again, without any divine intervention.