Back to basics
A return to previously held values of decency.
This became prominent in current language in the UK with a 1993 speech by UK Prime Minister John Major, although it had been used in everyday language long before that.
Major: "It is time to get back to basics: to self-discipline and respect for the law, to consideration for others, to accepting responsibility for yourself and your family, and not shuffling it off on the state."
It came to be used in the USA with the above explicit meaning during the 1970s. From The New York Times, March 1975:
"The style and tone of the churches have undergone a major adjustment, gradually turning toward a 'back-to-basics' approach. "