eys. Here is a still
smaller lock. This lock has a very peculiar keyhole, and I know at once
that there is no need of trying to unlock it with most of the keys which
I have spread out here. I recognize it at once as what is called a "Yale
lock." The key is thin, is bent in various ways, and along the edge has
several notches. Let us try a couple of these keys. This one seems to
fit very well to the grooves. It passes into the lock, but I cannot turn
the bolt. Let us try another. Yes, this seems to be the one that was
made by the locksmith to fasten and unfasten this lock.

[Illustration: Yale Lock and Key.]

A key then is simply something which unlocks the door or the gate, so
you may open it and pass inside. Now, there are a great many kinds of
keys. Sometimes a book is called a key to business. Perhaps another book
is called a key to the study of medicine; another the key to the study
of law. And so there may be a great many kinds of books which are called
keys. When properly used or studied they open the way for a clear
understanding of how to transact business, how to study medicine and how
to study law. And so there are various books that are keys to the
understanding of very, very many subjects. When you indicate to me the
kind of difficulty that you have to overcome, it would be reasonably
easy to indicate the kind of book you need in order successfully to meet
that difficulty.

When I find a book that teaches a boy good business habits and helps him
to become a good business man, I know that book was written with that
object in view. When I find a book that teaches one how to understand
the human system, the nature of disease and the character of the
remedies which are to be used when people are sick, I know that book was
written with a view to help people to understand the nature of disease
and the character of medicine. Just so it is with every other book. Each
is like the lock and the key, for the locks have inside a peculiar sort
of winding way, and when I find a key that exactly fits into this
winding passage I know immediately that the locksmith designed that the
key should fit into that particular lock and turn back the bolt.

Now, God wants to get into the human heart, and I find that God has a
key with which to unlock it. I do not think you would be long in
guessing what book God has made the key with which to unlock the human
heart. I think that every boy and girl would at once say that it is the
B