Because such things could sow error, create warring opinions, split the religion into sects, and disastrously cripple its power.

Mrs.
Eddy will do the whole of the explaining, Herself--has done it, in fact.
She has written several books.

They are to be had (for cash in advance), they are all sacred; additions to them can never be needed and will never be permitted.

They tell the candidate how to instruct himself, how to teach others, how to do all things comprised in the business--and they close the door against all would-be competitors, and monopolize the trade: "The Bible and the above--named book [Science and Health], with other works by the same author," must be his only text-books for the commerce--he cannot forage outside.
Mrs.Eddy's words are to be the sole elucidators of the Bible and Science and Health--forever.

Throughout the ages, whenever there is doubt as to the meaning of a passage in either of these books the inquirer will not dream of trying to explain it to himself; he would shudder at the thought of such temerity, such profanity, he would be haled to the Inquisition and thence to the public square and the stake if he should be caught studying into text-meanings on his own hook; he will be prudent and seek the meanings at the only permitted source, Mrs.
Eddy's commentaries.
Value of this Strait-jacket.