John Wesley had been publishing hymn collections for forty years before he made this one, and the 1780 book is the settled version of the project. Its most consequential feature is not any single text but the order. Wesley did not arrange the hymns by the church year, by scripture reference or by metre. He arranged them by the stages of a Christian life as Methodist preaching described it: the state of the natural person, the awakening, the turning, the assurance of forgiveness, the life of the believer, the struggle against remaining sin, and the hope of entire sanctification.
Read straight through, the book is therefore an argument. A convert taken through the sections in order has been taught the whole of Methodist doctrine without opening a work of theology, and Wesley says as much in his preface, describing the collection as a small body of experimental and practical divinity. Experimental in his usage means tested in experience rather than provisional, and the claim is that these hymns state what a believer will actually find to be the case.
The consequence is that Methodism inherited a doctrinal standard in verse. Where other Protestant bodies point to a confession when asked what they hold, Methodists have been able to point to hymns, and disputes about revising Charles Wesley's texts in later hymnals have accordingly been arguments about doctrine rather than about taste. That is unusual. Very few Christian bodies have let their poetry carry that much weight.