A number of private letters written by Melanchthon during and immediately after his conflict with Cordatus, however, reveal much animosity, not only against Cordatus, but against Luther as well. Nor do those written after Luther's disputation, June 1, 1537, indicate that he was then fully cured of his error. (357. 392. 407.) Moreover, in his _Loci_ of 1538 we read: "_Et tamen haec nova spiritualis obedientia (nova spiritualitas) necessaria est ad vitam aeternam._ And nevertheless this new spiritual obedience is necessary to eternal life." (21, 429.) Evidently, then, Melanchthon did not grasp the matter, and was not convinced of the incorrectness of his phraseology. Yet he made it a point to avoid and eliminate from his publications the obnoxious formula: "_Bona opera necessaria esse ad salutem._" At any rate, his essay on Justification and Good Works, of October 1537, as well as subsequent publications of his, do not contain it. In the _Loci_ of 1538, just referred to, he replaced the words _bona opera_ by the phrase _obedientia haec nova spiritualis,_--indeed, a purely verbal rather than a doctrinal change. Nor did it reappear even in the _Variata_ of 1540. In 1541, at Regensburg, Melanchthon consented to the formula "that we are justified by a living and efficacious faith--_iustificari per fidem vivam et efficacem._" But when Luther deleted the words "_et efficacem,_ and efficacious," Melanchthon acquiesced. (4, 499.) In the _Loci_ of 1543 he expunged the appendix "_ad salutem,_ to salvation." At the same time, however, he retained the error in a more disguised form, _viz._, that good works are necessary to retain faith. For among the reasons why good works are necessary he here enumerates also "the necessity of retaining the faith, since the Holy Spirit is expelled and grieved when sins against the conscience are admitted." (21, 775.) 143. Formula Renewed--Abandoned.