Besides, being a Jew, he had to be content with toleration, because in other countries even this was denied his race. "Is it not forbidden, according to the laws of your native city," he ask Lavater, "for your circumcised friend even to visit you in Zürich?" The French work of Bonnet he did not find so convincing, he said, as to cause his convictions to waver; he had read better defenses of Christianity written by Englishmen and Germans; also it was not original, but borrowed from German writings. The arguments were so feeble and so little tending to prove Christianity that any religion could be equally well or badly defended by them. If Lavater thought that a Socrates could have been convinced of the truth of Christianity by this treatise, he only showed what power prejudice exerts over reason.
If the evangelical consistory, before whom Mendelssohn offered to lay his letter for censorship before printing it, did not regret granting him permission to print whatever he pleased, "because they knew his wisdom and modesty to be such that he would write nothing that might give public offense," still he undoubtedly did give offense to many pious persons.
Mendelssohn's epistle to Lavater naturally made a great sensation. Since the appearance of Phædon, he belonged to the select band of authors whose works every cultivated person felt obliged to read. Besides it happened that the subject of the controversy was attractive at the time. The free-thinkers—by no means few at this time—were glad that at last some one, a Jew at that, had ventured to utter a candid word about Christianity. Owing to his obtrusiveness and presumptuous advocacy of Christianity, Lavater had many enemies. These read Mendelssohn's clever reply to the zealous conversionist with mischievous delight. The hereditary prince of Brunswick, who, as said above, was charmed with Mendelssohn, expressed (January 2, 1770) his admiration, that he had spoken "with such great tact and so high a degree of humanitarianism" upon these nice questions. Bonnet himself, less objectionable than his servile flatterer, admitted the justice of Mendelssohn's cause, and complained of Lavater's injudicious zeal. A letter of his dated January 12, 1770, was almost a triumph for Mendelssohn. He said that his dissertation, with which Lavater had desired to convert the Jew, had not been addressed to the honorable "House of Jacob," for which his heart entertained the sincerest and warmest wishes; much less had it been his intention to give the Jewish philosopher a favorable opinion of Christianity. He was full of admiration for the wisdom, the moderation, and the abilities of the famous son of Abraham. He indeed desired him to investigate Christianity, as it could only gain by being subjected to a close inquiry by the wise son of Mendel. But he did not wish to fall into Lavater's mistakes, and make it burdensome for him. However, in spite of his virtuous indignation, Bonnet perpetrated a bit of knavery against Mendelssohn. Lavater himself was obliged in a letter to publicly beg Mendelssohn's pardon for having placed him in so awkward a position, entreating him at the same time to attest that he had not intentionally been guilty of any indiscretion or perfidy. Thus Mendelssohn had an opportunity of acting magnanimously towards his opponent. On the subject proper under dispute, however, he remained firm; he did not surrender an iota of his Judaism, not even its Talmudical and Rabbinical peculiarities, and with every step his courage grew.
Mendelssohn did not wish to let pass this propitious opportunity of glorifying Judaism, which was so intensely contemned, and make it clear that it was in no way opposed to reason. Despite the warnings of timid Jews, to allow the controversy to lapse, so as not to stir up persecutions, he pointed out with growing boldness the chasm which Christianity had dug between itself and reason, whereas Judaism in its essence was in accord with reason. "The nearer I approach this so highly-esteemed religion," he wrote in his examination of Bonnet's "Palingénésie," "the more abhorrent is it to my reason." It afforded him especial delight when strictly orthodox Christians thought that they were abusing Judaism by declaring it to be equivalent to natural religion (Deism).
"Blessed be God, who has given unto us the doctrine of truth. We have no dogmas contrary to, or beyond reason. We add nothing, except commandments and statutes, to natural religion; but the fundamental doctrines of our religion rest upon the basis of understanding." "This is our glory and our pride, and all the writings of our sages are full of it."
Frankly Mendelssohn spoke to the hereditary prince of Brunswick of the untenability of Christian, and the reasonableness of Jewish, dogmas. He thought that he had not yet done enough for Judaism.
"Would to God, another similar opportunity were granted me; I would do the same.... When I consider what we ought to do for the recognition of the sanctity of our religion."
Those who had not wholly parted company with reason declared Mendelssohn to be in the right, and his defense to be just. They beheld with astonishment that Judaism, so greatly despised, was yet vastly superior to celebrated, official, orthodox Christianity. Through its noble son, Judaism celebrated a triumph. The unhappy ardor of Lavater, and the refined yet daring answer of Mendelssohn for a long time formed the topic of conversation in cultured circles in Germany, and even beyond its borders. The journals commented upon it, and noted every incident. Anecdotes passed backwards and forwards between Zürich and Berlin. It was said that Lavater had asserted that if he were able to continue for eleven days in a state of complete holiness and prayer, he would most positively succeed in converting Mendelssohn to Christianity. When Mendelssohn heard this saying—whether authentic or not it is characteristic of Lavater—he smilingly said, "If I am permitted to sit here in my armchair and smoke a pipe philosophically, I have no objections!" There was more talk of the contest between Mendelssohn and Lavater than of war and peace. Every fair brought pamphlets written in German and French, unimportant productions, which did not deserve to live long. Only a few were on Mendelssohn's side, the majority took the part of Christianity and its representatives against the "insolence of the Jew," who did not consider it an honor to be offered admission into the Christian community.
The worst of these was by a petty, choleric author, named John Balthasar Kölbele, of Frankfort-on-the-Main, who, from hatred of the Jews, or from distemper of body and soul, hurled such coarse insults against Mendelssohn, the rabbis, the Jews, and Judaism, that his very violence paralyzed his onslaught. Kölbele had on a previous occasion attacked Mendelssohn, and jeered at him by means of a lay figure in one of his forgotten romances. He desired to write, or said that he had written, an "Anti-Phædon" against Mendelssohn's "Phædon." His whole gall was vented in a letter to "Mr. Mendelssohn upon the affair of Lavater and Kölbele" (March, 1770). Against the assertions of Mendelssohn as to the purity of Judaism, he brought forward the calumnies and perversions of his brother in feeling, Eisenmenger. Mendelssohn's pure, unselfish character was known in almost all cultivated and high circles of Europe. Nevertheless, Kölbele cast the suspicion upon him of adhering to Judaism from self-interest, "because a Jewish bookkeeper is in a better position than a Christian professor, and the former besides derives some profit from attendance in the antechambers of princes." To Mendelssohn's asseveration that he would cling to Judaism all his lifetime, the malignant fool or libeler rejoined, "How little value Christians attach to the oath of a Jew!" Mendelssohn disposed of him in a few words in the postscript of a letter addressed to Lavater. Nothing more was required; Kölbele had condemned himself. Mendelssohn profited by these vilifying attacks, inasmuch as respectable authors, who in their hearts were not a little irritated by his independent and bold action, left him in peace, rather than be associated with Kölbele. Mendelssohn emerged victorious from this conflict, trifling only at first sight, which had lasted for nearly two years; he rose in public opinion, because he had manfully vindicated his own religion.