John's lack of religious conviction has been noted by contemporary chroniclers and later historians, with some suspecting that John was at best impious, or even atheistic, a very serious issue at the time. Contemporary chroniclers catalogued his various anti-religious habits at length, including his failure to take communion, his blasphemous remarks, and his witty but scandalous jokes about church doctrine, including jokes about the implausibility of the Resurrection. They commented on the paucity of John's charitable donations to the church. Historian Frank McLynn argues that John's early years at Fontevrault, combined with his relatively advanced education, may have turned him against the church. Other historians have been more cautious in interpreting this material, noting that chroniclers also reported John's personal interest in the life of St Wulfstan of Worcester and his friendships with several senior clerics, most especially with Hugh of Lincoln, who was later declared a saint. Financial records show a normal royal household engaged in the usual feasts and pious observances – albeit with many records showing John's offerings to the poor to atone for routinely breaking church rules and guidance. The historian Lewis Warren has argued that the chronicler accounts were subject to considerable bias and the King was "at least conventionally devout," citing his pilgrimages and interest in religious scripture and commentaries.

Historians suspected that John was at best what?