Allen’s book, “As a Man Thinketh” starts out :
“Mind is the Master power that molds and makes,
And Man is Mind, and evermore he takes
The tool of Thought, and, shaping what he wills,
Brings forth a thousand joys, a thousand ills:
He thinks in secret, and it comes to pass:
Environment is but his looking-glass.”
The book was published in 1903. It was described by Allen and was the early leader of the many self-help books that followed. Drawing insight from Proverbs 23:6-8 in the King James version of the Bible the book focuses on the power of thought.
The book shows how application of the principle is a choice made by each individual and that it leads to both good and bad conditions being the results of those thoughts.
Allen said is was "A book that will help you to help yourself", "A pocket companion for thoughtful people", and "A book on the power and right application of thought.
"Men do not attract what they want, but what they are."
"A man is literally what he thinks, his character being the complete sum of all his thoughts."
"Cherish your visions. Cherish your ideals. Cherish the music that stirs in your heart, the beauty that forms in your mind, the loveliness that drapes your purest thoughts, for out of them will grow all delightful conditions, all heavenly environment, of these, if you but remain true to them your world will at last be built."
"The soul attracts that which it secretly harbors, that which it loves, and also that which it fears. It reaches the height of its cherished aspirations. It falls to the level of its unchastened desires,– and circumstances are the means by which the soul receives its own." 
"Men are anxious to improve their circumstances, but are unwilling to improve themselves, they therefore remain bound."
"Every action and feeling is preceded by a thought."
"Right thinking begins with the words we say to ourselves."
"Circumstance does not make the man, it reveals him to himself."
"You cannot travel within and stand still without.