That a teacher of the gospel should first be a partaker of it is a simple truth, but at the same time a rule of the most weighty importance… No amount of fees paid to learned doctors, and no amount of classics received in return, appear to us to be evidences of a call from above. True and genuine piety is necessary as the first indispensable requisite; whatever “call” a man may pretend to have, if he has not been called to holiness, he certainly has not been called to the ministry… Conversion is a sine qua non in a minister. Ye aspirants to our pulpits, “ye must be born again.”… Believe me, it is no child’s play to “make your calling and election sure.” The world is full of counterfeits, and swarms with panderers to carnal self-conceit, who gather around a minister as vultures around a carcass. Our own hearts are deceitful, so that truth lies not on the surface, but must be drawn up from the deepest well. We must search ourselves very anxiously and very thoroughly, lest by any means after having preached to others we ourselves should be castaways.
Lectures to My Students (Pasadena, TX; Pilgrim; 1990) p. 3-4