Harris used to preach regularly from the grave of his Grandparents because he was not allowed to preach in the Church. John Wesley had to preach from his father's tomb for the same reason.
Harris and Rowland had the uninhibited and compelling urge to preach the Gospel. Crowds flocked to hear them; Harris writes that between 400 and 2,000 would hear him speak. Some future leaders were being saved under Harris’ ministry. Howel Davies was converted at one of his meetings in 1737 and he went on to be a curate of Griffith Jones, later becoming the ‘Apostle of Pembrokeshire.’ In 1738 William Williams of Pantycelyn, the hymn writer, accepted Jesus after hearing Harris in Talgarth churchyard. Rowland, Harris, Williams and Davies were the four leaders of the Great Awakening in Wales, and they worked together for many years.