Testament ought to be ministered as they were instituted by Christ, and nothing added to or taken from them,’ that ‘the mass is abominable idolatry,’ and that ‘there is no purgatory, and there are no bishops unless they preach themselves.’ Winram, the sub-prior, first disputed with Knox, but left the conclusion of the argument to Arbuckle, a grey friar, whom Knox, according to his own narrative—the only account preserved—easily overcame by a combination of texts, logic, and ridicule. Knox refers, for his share in the debate, to ‘a treatise he wrote in the galleys,’ containing the pith of his doctrine and the confession of his faith. This has not been preserved, unless the reference be to the letter he wrote to his brethren in Scotland in 1548, when he sent them Balnaves's ‘Confession and Treatise on Justification.’ The friars attempted to stifle a voice they could not answer by occupying the pulpit at St. Andrews Sunday about, but Knox evaded this device by preaching on the weekdays and protesting that if the friars preached in his absence the people ought to suspend their judgment till they heard him again. The effect of his preaching was that many in the town as well as the castle accepted the reformed doctrine, and communicated at the Lord's Table after the reformed rite. On 31 June 1547 the French galleys, under Strozzi, prior of Capua, appeared in the Forth and besieged the castle on 18 July. The regent soon after joined in the siege on the land side. On 31 July the castle capitulated. By the terms of the capitulation the prisoners, of whom Knox was one, were to be sent to France in the galleys, and either liberated there or sent to any other country they chose except Scotland. They were taken to Fécamp, a port of Normandy, and thence up the Seine to Rouen, but, in breach of the terms of their surrender, were dispersed in several prisons. Knox remained with the galleys, which sailed to Nantes and lay in the Loire all the winter. In the summer of 1548 the galleys returned to the Scotch coast. The prisoners' treatment, though strict, was not very rigid.
Balnaves composed his ‘Treatise on Justification by Faith’ in the castle of Rouen, and managed to send it to Knox in the galley Notre Dame. Knox digested it into chapters and forwarded it, with an epistle, to the congregation of the castle of St. Andrews in 1548. It reached the hands of his friends at Ormiston, but was first published in 1584 by the French printer Vautrollier, who explains, in a dedication to Lady Sandilands, the mother of Knox's pupil Cockburn, that it had been unsuccessfully sought for by Knox after his return to Scotland, and accidentally recovered by Richard Bannatyne [q. v.], Knox's amanuensis, in the hands of some children at play. As the earliest of his known writings, it is remarkable for the clearness with which it propounds the Lutheran doctrine that ‘faith is only justifiable before God, without all aid and merit of our works.’ In February 1549 his own release was effected, probably by the intercession of Edward VI, and he came to England.
On 7 April 1549 Knox received 5l., ‘by way of reward, from the king's privy council,’ and was sent by the council to preach at Berwick, where he remained two years, attracting a large congregation. While there he prepared and probably issued a tract, of which the first edition extant was published in 1554: ‘A Declaration what true Prayer is, how we should pray, and for what we should pray.’ On 4 April 1550 he was summoned, at the instance of Tunstall, the Romanist bishop of Durham, to answer for having upheld in his preaching ‘that the mass was idolatry.’ His defence, afterwards printed along with a letter to Mary of Guise, the queen regent, in 1556, was a syllogistic argument: ‘All service invented by the brain of man in the religion of God, without his own express command, is idolatry. The mass is invented by the brain of man without the command of God; therefore it is idolatry.’ He explained that the mass was abomination, and concluded by distinguishing the Lord's Supper of the protestants at the communion-table from the sacrifice of the mass, which the priest offered at the altar. Neither Tunstall nor any one else answered him. Probably most of the council were lukewarm or favourable. Nothing came of this, his first prosecution.
A tract of two or three pages, containing ‘in a Sum, according to the Holy Scriptures, what opinions we Christians haif of the Lordis Supper, callit The Sacrament of the Bodie and Blude of our Saviour Jesus Christ,’ printed without date, was probably issued in the same year for general circulation. About the end of 1550 he removed to Newcastle, where he served as preacher in the church of St. Nicholas, and in autumn 1551 he was appointed one of six royal chaplains, with a salary of 40l., of which the first payment was made by the privy council on 27 Oct. 1552. While at Newcastle he denounced from the pulpit the execution of Somerset. As king's chaplain he took part in the revision of the second prayer-book of Edward VI, issued 1 Nov. 1552, and is credited with the ‘black rubric,’ which explained that the act of kneeling meant no adoration of the bread and wine, ‘for that idolatry is to be abhorred