When Gram Parsons joined the Byrds [and David Crosby left] — Philip Jenkins argues in "When Evangelicals Were Cool" — it helped open the popular culture to hear the gospel:
Quite unintentionally, the Byrds also revived and legitimized Christian themes in music for an audience wholly unaccustomed to them. If you want to revive America's roots music, it's hard to do so without incorporating hymns, gospel and Christian songs, and Sweetheart of the Rodeo featured such evocative classics as I am a Pilgrim and The Christian Life.
In 1969, they recorded the Art Reynolds Singers song Jesus is Just Alright with Me, which became an anthem for the emerging Jesus People. Plenty of other artists jumped on the bandwagon, recording or adapting Christian roots — and that is quite distinct from the contemporary emergence of avowedly Christian contemporary music. (Christian rock largely dates from Larry Norman's 1969 album Upon This Rock). The language of pilgrimage, redemption and sin entered rock music, as did Satan himself: in 1970, the Grateful Dead issued Friend of the Devil.
Suddenly, young people who knew nothing whatever about the American religious heritage were exposed to this music, in highly accessible rock/country fusion styles, played by hip musicians with long hair and beards. Along the way, they also heard key evangelical messages, which suddenly became cool and contemporary.
And that, I suggest, is a major reason why those Christian movements were suddenly able to find young audiences open and receptive to their messages. ....
RealClearReligion - When Evangelicals Were Cool