When the seminary opened in the autumn, he was back in his place. One of the duties which fell to him was to preach a missionary sermon before the Society of Inquiry. He did this so well that the students by vote expressed a desire that the sermon should be published. In his Journal he notes that the preparation of this discourse “strengthened his determination to give himself to this work.” Before the Christmas recess Dr. J. Leighton Wilson, one of the secretaries of the Presbyterian Board of Foreign Missions, visited the seminary, and in conference did much to stimulate the missionary spirit. He found in Mateer an eager and responsive listener. On the 12th of December Mateer wrote a long letter to his mother, in which he expresses feeling, because without warrant some one had told her that he had offered himself to the Foreign Board. He says, “I am not going to take such an important step without informing you of it directly and explicitly.” Then he proceeds to tell her just what was his attitude at that time: I have thought of the missionary work this long time, but not very seriously until within the last couple of years. Ever since I came to the seminary I have had a conviction to some degree that I ought to go as a missionary. That conviction has been constantly growing and deepening, and more especially of late. I have about concluded that so far as I am myself concerned it is my duty to be a missionary. I have thought a great deal on this subject and I think that I have not come to such a conclusion hastily. It has cost me very considerable effort to give up the prospects which I might have had at home. The matter in almost every view you can take of it involves trial and self-denial. I need great grace,—for this I pray. But even if I have prospects of usefulness at home, surely nothing can be lost in this respect by doing what I am convinced is my duty. Indeed, one of the encouraging features, in fact the great encouragement, is a prospect of more extended usefulness than at home. This may seem not to be so at the first view, but a more careful consideration of all the aspects of the case will, I think, bring a different conclusion. The letter is very full, and lays bare his whole mind and heart as he would be willing to do only to his mother. It is a revelation of this strong, self-reliant, mature but filial-spirited and tenderly thoughtful young Christian man and prospective minister, to a mother whom he recognized as deserving an affectionate consideration such as he owed to no other created being.