These letters were eventually compiled by one 'Mary Strong' and published in 1948. It is still in print and very popular with those attracted to spiritual living.
Found the first letter online, here is some of it:
Let us consider again what our daily living is, this
human living without thought; the conduct of people, the
philosophy needed to live upon earth, to live intelligently, the
mystery of pleasure and pain. First it appears that we are
spoiled from lack of discipline, seif-discipline. We are ignorant,
too, and full of wild emotions, savage dislikes, greed, pride;
pride of family, of race, community and nation.
This emotional fever-bag is our danger, for left to itself,
inflated by angry argument, it is destructive and overpowers
the balance of clear thinking. Through it we are influenced
and swayed by passing events, the daily news and all the
harm of misinformation. When possessed by states that are
ungoverned, even while we carry our outward poise, there is
a kind of lawlessness that swings to inertia, a what's-the-use
attitude of mind, a refusal to make an efiort which is a kind
of lawlessness also. A child asks, Why is it necessary to have
law and discipline? Because it is needful to establish a balanced
order of conduct. Think for a moment of yourselves as raw
material; through your acceptance or rejection of a thought,
an idea, you establish your lives, your individualities. Emotion
is as wild and unpredictable as the weather and must be faced
and dominated. No wonder the ancients called it the devil,
for at times it will run away with you, weaken your resolves,
loosen your armor and plunge you into hell. Here is where
pain often comes in and is indeed the drill sergeant. You have
seen how many wild natures have been touched and softened
by pain and sorrow. But why go that way to illumination?
You who have started on this strange and beautiful journey,
who have sensed immortality and touched it, have opened a
door into a place where the mystery of life will be simplified
for you if you will obey these promptings from within.