Another Dominican, James van Hoogstraten, prior at Cologne, who had already figured as the prime zealot in the affair about Reuchlin, which he was still prosecuting, now demanded, in his preface to a pamphlet on that subject, that Luther should be sent to the stake as a dangerous heretic.
But a far more important, and to Luther an utterly unexpected opponent, appeared in the person of John Eck, professor at the university of Ingolstadt, and canon at Eichstädt. He was a man of very extensive learning in the earlier and later Scholastic theology of the Church; he was a sharp-witted and ready controversialist, and he knew how to use his weapons in disputations. He was fully conscious of these gifts, and made a bold push to advance himself by their means, whilst troubling himself very little in reality about the high and sacred issues involved in the dispute. He sought to keep on friendly and useful relations with other circles than those of Scholastic theology, such as with learned Humanists, and a short time before, with Luther himself and his colleague Carlstadt, to whom he had been introduced through a jurist of Nüremberg named Scheuerl. Luther, after the publication of his theses, had written a friendly letter to Eck. What then was his surprise to find himself attacked by Eck in a critical reply entitled 'Obelisks.' The tone of his remarks was as wounding, coarse, and vindictive as their substance was superficial. They aimed a well-meditated blow, by stigmatising Luther's propositions as Bohemian poison, mere Hussite heresy. Eck, when reproached for such a breach of friendship, declared that he had written the book for his bishop of Eichstädt, and not with any view of publication.
Luther himself, loud as was his call to battle in his theses, had still no intention of engaging in a general contest about the leading principles of the Church. He had not yet realised the whole extent and bearings of the question about indulgences. Referring afterwards to the rapid circulation of his theses through Germany, and to the fame which his onslaught had earned him, he says, 'I did not relish the fame, for I myself was not aware of what there was in the indulgences, and the song was pitched too high for my voice.' People far and wide were proud of the man who spoke out so boldly in his theses, while the multitude of doctors and bishops kept silence; but he still stood alone before the public, confronting the storm which he had aroused against himself. He did not conceal the fact, that now and then he felt strange and anxious about his position. But he had learned to take his stand singly and firmly on the word of Scripture, and on the truth which God therein revealed to him and brought home to his conviction. He was only the more strengthened in that conviction by the replies of his opponents; for he must well have been amazed at their utter want of Scriptural reference to disprove his conclusions, and at the blind subservience with which they merely repeated the statements of their Scholastic authorities. The arrogant reply of Prierias, his opponent of highest rank, seemed to him particularly poor. In confident words Luther assures his friends of his conviction that what he taught was the purest theology, that what he upheld and his opponents attacked, was a revelation direct from God. He knew too, that, in the words of St. Paul, he had to preach what to the holiest of the Jews was a stumbling-block, and to the wisest of the Greeks foolishness. He was none the less ready to do so, that Jesus Christ, his Lord, might say of him, as He said once of that Apostle, 'I will show him how great things he must suffer for my name's sake.' Luther's enemies in the Romish Church have thought to see in these words an instance of boundless self-assertion on the part of an individual subject.
From henceforth Luther, while pursuing with unabated zeal his active duties at the university and in the pulpit at Wittenberg, and taking up his pen again and again to write short pamphlets of a simple and edifying kind, occupied himself untiringly with controversial writings, with the object partly of defending himself against attacks, partly of establishing on a firm basis the principles he had set forth, and of further investigating and making plain the way of true Christian knowledge. He first addressed himself to German Christendom, in German, in his 'Sermon on Indulgences and Grace.' His inward excitement is shown by the vehemence and ruggedness of expression which now and henceforth marked his polemical writings. It recalls to mind the tone then commonly met with not only among ordinary monks, but even in the controversies of theologians and learned men, and in which Luther's own opponents, especially that high Roman theologian, had set him the example. In Luther we see now, throughout his whole method of polemics, as we shall see still more later on, a mighty, Vulcanic, natural power breaking forth, but always regulated by the humblest devotion to the lofty mission that his conscience has imposed upon him. Even in his most vehement outbursts we never fail to catch the tender expressions of a Christian warmth and fervour of the heart, and a loftiness of language corresponding to the sacredness of the subject.
In the midst of these labours and controversies, Luther had to undertake a journey in the spring of 1518 (about the middle of April) to a chapter general of his Order at Heidelberg, where, according to the rules, a new Vicar was chosen after a triennial term of office. His friends feared the snares that his enemies might have prepared for him on the road. He himself did not hesitate for a moment to obey the call of duty.
The Elector Frederick, who owed him at least a debt of gratitude for having helped to keep his territory free from the rapacious Tetzel, but who, both now and afterwards, conscientiously held aloof from the contest, gave proof on this occasion of his undiminished kindness and regard for him, in a letter he addressed to Staupitz. He writes as follows:—'As you have required Martin Luder to attend a Chapter at Heidelberg, it is his wish, although we grudge giving him permission to leave our university, to go there and render due obedience. And as we are indebted to your suggestion for this excellent doctor of theology, in whom we are so well pleased, … it is our desire that you will further his safe return here, and not allow him to be delayed.' He also gave Luther cordial letters of introduction to Bishop Laurence of Wurzburg, through whose town his road passed, and to the Count Palatine Wolfgang, at Heidelberg. From both of these, though many had already declaimed against him as a heretic, he met with a most friendly and obliging reception.
His relations, moreover, at Heidelberg with his fellow-members of the Order, and, above all, with Staupitz, remained unclouded. Staupitz was re-elected here as Vicar of the Order; the office of provincial Vicar passed from Luther to John Lange, of Erfurt, his intimate friend and fellow-thinker. The question about indulgences had not entered at all into the business of the chapter. But at a disputation held in the convent, according to custom, Luther presided, and wrote for it some propositions embodying the fundamental points of his doctrines concerning the sinfulness and powerlessness of man, and righteousness, through God's grace, in Christ, and against the philosophy and theology of Aristotelian Scholasticism. He attracted the keen interest of several young inmates of the convent who afterwards became his coadjutors, such as John Brenz, Erhardt Schnepf, and Martin Butzer. They marvelled at his power of drawing out the meaning from the Scriptures, and of speaking not only with clearness and decision, but also with refinement and grace. Thus his journey served to promote at once his reputation and his influence.
On his return to Wittenberg on May 15, after an absence of five weeks, he hastened to complete a detailed explanation in Latin of the contents of his theses, under the title of 'Solutions,' the greatest and most important work that he published at this period of the contest.
The most valuable fruit of the controversy so far as regards Luther and his later work, and evidence of which is given in these 'Solutions,' was the advance he had made, and had been compelled to make, in the course of his own self-reasoning and researches. New questions presented themselves: the inward connection of the truth became gradually manifest: new results forced themselves upon him: his anxiety to solve his difficulties still continued.
Luther in his theses, when speaking of the call of Jesus to repentance, had never indeed admitted that the sacrament of penance enjoined by the Church, with auricular confession and the penances and satisfactions imposed by the priest, was based on God's command or the authority of the Bible. He now openly acknowledged and declared that these ecclesiastical acts were not enjoined by Christ at all, but solely by the Pope and the Church.