First of all, a knowledge of the office. One must know what it means to be a servant of Christ, to be the mouth of the Lord, to proclaim that great gospel, to teach ignorant men the way of salvation, to be instrumental in delivering men from the devil, and to lead them to Christ. One must know that it consists in comforting those who mourn, stirring up the indolent, bringing back those who have strayed, exposing hypocrites and temporal believers to themselves, defending the truth against error, rebuking the ungodly, helping to keep out or expelling from the church those who lead offensive lives, and adorning the church, so that by the holiness of those who profess the truth she would bring glory to Christ. One must know that it consists in being an example and in being able to give an account of the souls entrusted to him. How can he who is neither thoroughly acquainted with these matters, nor perceives the weightiness of it all, nor takes this to heart, have intentions to be faithful? All of this must be known, considered, and experienced in order to be conscious of one's calling.
Secondly, there must be some knowledge of one's aptitude for this work. A fundamental knowledge of divine truths and thus being satisfied with a speculative knowledge of these is not sufficient. Rather, one must experience the power of these truths in his own heart, having been converted thereby. He will thus be able to speak from his own experience. He must also have the aptitude to clearly express his thoughts, and must have a voice which is capable of being heard by others. Even though the most qualified person must say, "Who is sufficient for these things?" (2 Cor. 2:16), one must nevertheless be conscious of some aptitude. Shortly we shall consider this aptitude more comprehensively.
Thirdly, there must be an extraordinary love a) for Christ and a desire to make Him known; b) for the church to present her as a chaste virgin to Christ (2 Cor. 11:2), and to cause her to shine forth with light and holiness to the honor of God; c) for the souls of the unconverted to snatch them from the fire, as well as of the converted to strengthen, comfort, and continually provide them with spiritual food.
Fourthly, one must be willing to deny all that is of the world, such as honor, material goods, yes and even life itself. If someone is of low social status and wishes to become someone of renown or to acquire material goods by way of the ministry, his objective is entirely wrong. He would be much happier as a shoemaker, for in my opinion there is no man more abominable than an unregenerate minister who uses the holy things of God to his own advantage.
Fifthly, there must be a great desire for this work (1 Tim. 3:1). There must be continual stirrings to give oneself to the Lord by way of this work, and there must be a concern about whether or not one is called. There must be anxiety when ulterior motives are perceived in the heart which in turn causes one to entertain the thought to refrain from this work; or when the heaviness of the task, and a sense of inability causes one to look up against this work, engendering a desire to be relieved from this work, as with Moses and Jeremiah. The stirrings will nevertheless persist and overcome the objections. This in turn will give him more liberty before the Lord and he will find himself more willing than beforehand because by the objections he will have a clearer view of the motives of his heart. Then his heart does not condemn him, but rather convinces him of his sincerity in this matter.