According to Mark Noll, a prominent scholar of Church history and an evangelical himself, the “best current definition of EVANGELICALISM” (Protestant Evangelicalism) has 4 “Key Marks”:

(1)  Biblicism  (a reliance on the Bible as the ultimate religious authority),

(2)  Conversionism  (a stress on the New Birth),

(3)  Activism  (an energetic, individualistic approach to religious duties and social involvement), and

(4)  Crucicentrism  (a focus on Christ’s redeeming work as the heart of essential Christianity) 

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This information is from Mark Noll’s The New Shape of World Christianity (IVP Academic, 2009-Kindle version).  Noll is quoting another prominent church historian, David Bebbington who, as best as I can tell, made this statement around 1989.

I hope you don’t find this detailing tedious.  We do our best to say where “key” info comes from.  “Evangelical” is one of those Christian words that gets thrown around a lot without people knowing what it really means.  There is a long fascinating history of Christianity’s march through the centuries, and it is usually admitted that the spread of Christianity through the last 200 years or so was due largely from Evangelicals (and to a certain extent Roman Catholics).  Realize 3 things:  (1) “Evangelical” is an umbrella term for many denominations, or subsets of groups within other denominations. (2) Many Evangelicals “spell out” what they believe in greater detail than the 4 “keys.”  (3) For many Christian groups, “evangelical” has replaced “fundamentalist,” that term being considered “older” and unnecessarily “stricter.”

(“Crucicentrism” refers to the importance of the Cross of Christ and his death as necessary for humans who are sinners in need of salvation.)