Already in his preface to Balnaves's treatise on Justification, the first of his printed productions so far as can be traced, he had written a summary of his belief on that great central doctrine; and in his disputation with Arbuckle in St. Andrews, he had been truly charged with holding the following opinions--viz. first, man may neither make nor devise a religion that is acceptable to God, but is bound to observe and keep the religion that from God is received without chopping or changing thereof; second, the sacraments of the New Testament ought to be ministered as they were instituted by Christ Jesus and practised by the apostles, nothing ought to be added to them, nothing ought to be diminished from them; third, the mass is abominable idolatry, blasphemous to the death of Christ, and a profanation of the Lord's Supper. When therefore he began his labours at Berwick he set himself to the proclamation of the great truths which radiate from the priesthood of Christ; and in his dispensation of the supper he followed an order of his own, which was not improbably the same as he had adopted in the Castle of St. Andrews. This is put beyond dispute by his letter to the congregation of Berwick, written probably about the close of 1552, and the fragment entitled "The Practice of the Lord's Supper used in Berwick-upon-Tweed by John Knox, preacher to the congregation of the Church there," both of which are to be found in {33} Dr. Lorimer's Appendix. The matter is of more than mere antiquarian interest, and we may therefore make one or two extracts from the more important of these documents.