In a certain sense a minister selects his own congregation. If, in beginning a series of meetings, I advertise that I will speak on astronomy, I naturally draw a number of people who are interested in astronomy. Among them there may be those who have taken a course in the subject, and are up to date on the latest discoveries. Therefore if I make some misstatement or show ignorance of the subject on which I presume to preach, these persons are likely to go away feeling that I know nothing of what I am speaking, and suspect that I do not know anything about religion either.
If I speak on evolution and again reveal my ignorance, I am likely to eliminate from my congregation all who are interested in that subject, and who perhaps have studied it.
If I speak on current events and use unsupported quotations from "yellow" newspapers, I may lose from my audience all serious students of world affairs.
If I use poor English, many who are careful of their speech will regard me as unfitted to teach others. I thus gradually eliminate from my congregations all who are above me intellectually, and I have left only those who are below my level.
It is not possible for a minister to know everything about everything. He should be careful, however, not to get in beyond his depth. Whenever a minister speaks on any subject, he should know enough concerning it to command the respectful attention of those who really know. If he is not sure that he knows, he should, before speaking on any scientific subject, submit his lecture for critical correction to one who is an expert in that particular field. Many a man who is not able to do this, can get along very well by knowing enough to know what not to say.