Influenced by the Moravians the Wesleys joined in a 'Religious Society' in London, and in May 1738 both underwent a profound spiritual experience. John famously described this in his Journal for 24 May 1738
In the evening I went unwillingly to a society in Aldersgate Street, where one was reading Luther and preface to the Epistle to the Romans. About a quarter to nine, while he was describing the change which God works in the heart through faith in Christ, I felt my heart strangely warmed. I felt I did trust in Christ, Christ alone for salvation, and an assurance was given me that he had taken away my sins, even mine and saved me from the law of sin and death.
Three days earlier, following his own 'conversion', Charles had written a hymn
Where shall my wondering soul begin
How shall I all to heaven aspire?
For the following half-century such hymns flowed from Charles' pen (it is estimated he wrote over 6,000), while John was the organising genius who turned a spontaneous movement into structured body which became the origin of today's world-wide Methodist Church.