Metaphorically speaking, a person's ideas must be the building he lives in - otherwise there is something terribly wrong.

Just as a candle cannot burn without fire, men cannot live without a spiritual life.

Man is obviously made for thinking. Therein lies all his dignity and his merit; and his whole duty is to think as he ought.

The first duty of a man is to think for himself

I consider that a man’s brain originally is like a little empty attic, and you have to stock it with such furniture as you choose.

Man’s mind is his basic tool of survival. Life is given to him, survival is not. His body is given to him, its sustenance is not. His mind is given to him, its content is not. To remain alive, he must act, and before he can act he must know the nature and purpose of his action. He cannot obtain his food without a knowledge of food and of the way to obtain it. He cannot dig a ditch – or build a cyclotron – without a knowledge of his aim and of the means to achieve it. To remain alive, he must think.
“But to think is an act of choice. The key to what you so recklessly call ‘human nature,’ the open secret you live with, yet dread to name, is the fact that man is a being of volitional consciousness. Reason does not work automatically; thinking is not a mechanical process; the connections of logic are not made by instinct. The function of your stomach, lungs, or heart is automatic; the function of your mind is not. In any hour and issue of your life, you are free to think or to evade that effort. But you are not free to escape from your nature, from the fact that reason is your means of survival – so that for you, who are a human being, the question ‘to be or not to be’ is the question ‘to think or not to think.’ . . .
“Man has no automatic code of survival. His particular distinction from all other living species is the necessity to act in the face of alternatives by means of volitional choice. . . Man must obtain his knowledge and choose his actions by a process of thinking, which nature will not force him to perform. Man has the power to act as his own destroyer – and that is the way he has acted through most of his history (pages 1012-1013).

If men lived like men indeed, their houses would be temples — temples which we should hardly dare to injure, and in which it would make us holy to be permitted to live; and there must be a strange dissolution of natural affection, a strange unthankfulness for all that homes have given and parents taught, a strange consciousness that we have been unfaithful to our fathers honor, or that our own lives are not such as would make our dwellings sacred to our children, when each man would fain build to himself, and build for the little revolution of his own life only.

men’s actions are the best guides to their thoughts

The key to every man is his thought. Sturdy and defying though he look, he has a helm which he obeys, which is the idea after which all his facts are classified. He can only be reformed by showing him a new idea which commands his own.

Man, by thinking, can bring into his experience whatsoever he desires — if he thinks correctly, and becomes a living embodiment of his thoughts. This is not done by holding thoughts but by knowing the Truth.

Life consists of what man is thinking about all day.

All that we are is the result of what we have thought: it is founded on our thoughts and made up of our thoughts. If a man speak or act with an evil thought, suffering follows him as the wheel follows the hoof of the beast that draws the wagon.... If a man speak or act with a good thought, happiness follows him like a shadow that never leaves him.

It is necessary for the perfection of human society that there should be men who devote their lives to contemplation.

Every man is what he is, because of the dominating thoughts which he permits to occupy his mind.