Traditionally, to get religion is (1) to become religious, or (2) to end one’s immoral behavior. The phrase still carries those definitions, but it’s also used more figuratively to mean (1) to get serious about an issue and devote proper attention to it, and (2) to reform one’s view toward something. The idiom is usually followed by a preposition; about and on work best.
The derivation of the modern definition of get religion is obvious. To get religion in the older sense is to see the light of God, set aside one’s wanton ways, and get serious about living morally. The modern sense of get religion denotes a similar getting-serious process, but without the God part.
The OED lists get religion as an American idiom, but we’ve found several examples from elsewhere in the English-speaking world. The oldest examples of the modern sense of get religion in searchable texts are apparently from the 1960s, though we could be missing some older ones.
He was sure this girl wouldn’t get religion and act that way in front of people. [Know Nothing, Mary Lee Settle (1960)]
It is to get drunk every week for years, then “get religion” and stop drinking, start doing church work. [Life magazine (1960)]
It’s nice to see that the Ford campaign is getting religion on the defense issue. [Wall Street Journal (1976) (pay-per-view content)]
At age 36, advised by a life insurance carrier that my future was not insurable, I got religion about fitness. [Ocala Star-Banner (1990)]
President Obama treated deficit reduction mostly as a pesky afterthought, but then he got religion after the 2010 election shellacking that gave Republicans control of the House. [USA Today]
The Army gets religion about improving its handling of returning National Guard troops [Oregon Live]
In the early 1990s, after the new national Toxics Release Inventory had pegged it as America’s—and arguably the world’s—leading polluter, DuPont started toget religion about going green. [Green to Gold, Daniel Esty and Andrew Winston]
It wasn’t until the very end of his term that Rae appeared to get religion on spending control. [London Free Press]