Philosophy.SE, this is my first time being here, hence please pardon my inexperience of phrasing the question.
I was discussing the moral philosophy of Kant vs the moral philosophy of the Christian religion on "doing good things" and such with one of my Christian friends. I myself adhere to Kant's views due to my early exposure to The Critique of Pure Reason. I told my friend that you act due to the categorical imperative, and he doubted that categorical imperative could define the term "morally good" without introducing a higher deity. Here was where I stuck, I am not very sure how Kant's universality argument circumvents this question.
Have Kant ever defined "morally good" anywhere in his works? Thanks in advance.