The phrase was used by John Wesley to describe the vital, inward religion of faith and love which was a feature of his own 'conversion' and which he always longed for others to share. He asserted that 'This experimental knowledge [of God], and this alone, is true Christianity,' and in his preface to the 1780 Collection of Hymns described the book as 'a little body of experimental and practical divinity'. In the eighteenth century 'experimental' carried the meaning 'experiential', but in a scientific context was beginning to be used in the sense of actual experiment, putting a conviction to a practical test. Wesley certainly wished to convey both meanings. The words from Luther's 'Preface to the Epistle to the Romans' which he heard read at the Aldersgate meeting on 24 May 1738 offer a good insight into his understanding of the term: 'Faith is a living, daring confidence in God's grace, ... a living, busy, active, mighty thing, ... so it is impossible for it not to do good works incessantly.' In his sermon on 'The Witness of the Spirit' Wesley asserted that experience was not sufficient to prove a doctrine unsupported by Scripture, but was sufficient to confirm a doctrine grounded in Scripture. It has become part of twentieth century Methodist orthodoxy to see experience as one side of the 'Wesleyan quadrilateral'.