Confused by the meaning and construction of a sentence

Question

Help me comprehend the meaning and construction of this sentence:

For as a person thinketh in his subconscious mind, so he is.

Basically first part of the sentence is the problem to me. What "for as" means here?

Also, the word thinketh? I couldn't find it anywhere else.

Here is the full paragraph:

This book is designed to teach you that your habitual thinking and imagery mold, fashion and create your destiny. For as a person thinketh in his subconscious mind, so he is.

(source: The Power of Your Subconscious Mind by Dr. Joseph Murphy)

Answer 1

This is fake early English, in the style of the Bible or Shakespeare.

"Thinketh" is the old form of "thinks"

The structure is similar to expressions in the King James Bible. The word "for" links this sentence into the paragraph. It is giving a reason for habitual thinking, etc.

The word "as" is saying that two things are alike. His subconscious thinking = him.

Compare

As the crow flies, so does an arrow. (They fly the same way, in a straight line)

The style here is "elevated". It is meant to sound highly formal, very old fashioned, and may be modified from an actual Bible quote.

Answer 2

The word thinketh is an archaic verb. We don't normally see verbs conjugated using -eth unless we are reading very old texts.

The text you cited is actually a quote from the book of Proverbs in the Old Testament.

For as he thinketh in his heart, so is he (Prov. 23:7a, King James Version)

More modern translations of the Bible translate this verse in more contemporary language:

For as he thinks in his heart, so is he (Modern English Version)

The proverb is often interpreted as alluding to the fact that our character is largely defined by the thoughts that we have. In the case of this particular proverb, the fuller context is saying that we should not dine with people who are not generous, because their stingy attitudes are part of who they are, and they only offer food begrudgingly:

Do not eat the bread of a selfish man, or desire his delicacies; for as he thinks within himself, so he is. He says to you, “Eat and drink!” But his heart is not with you. (Prov. 23: 6-7, New International Version)

Don’t eat the food of selfish people; don’t be greedy for their fine foods. Selfish people are always worrying about how much the food costs. They tell you, “Eat and drink,” but they don’t really mean it. (New Century Version)

That little snippet you quoted has been used as the title of a book. From a synopsis on Amazon:

"As a Man Thinketh" is a literary essay by James Allen, published in 1903. It was described by Allen as "...dealing with the power of thought, and particularly with the use and application of thought to happy and beautiful issues."

As for your question about the meaning of "for as", that could be rephrased as "because the way". We might paraphrase the entire sentence like this:

Because the way a person thinks in his heart, that is the way he [truly] is.