The human intellect has not ...

The human intellect has not been able to conceive of anything more noble and sublime in the history of the world than the teachings of the Upanishads.
 Sivananda

Quotes from the same author

The mental ability to concentrate is inherent to all; it is not extraordinary or mysterious. Meditation is not something that a Yogi has to teach you; you already have the ability to shut out thoughts.
 Sivananda
Never worry. Be ever cheerful. Always laugh and smile. You can use the following powerful autosuggestion: "Mr. Worry, goodbye to you. I am a different person now. I am made of sterner stuff." Worry will now be afraid to show his face to you. You can then remove the worries of many of your friends.
 Sivananda
The impersonal aspect [of God] (Nirakara, Nirguna) is called Brahman, or 'unknowable' by Herbert Spencer, 'will' by Schopenhauer, Absolute Noumenon by some 'substance' by Spinoza. The personal aspect (Sakara) of that Being is termed 'Ishvara' or Allah, Hari, Jehova, Father in Heaven, Buddha, Siva, etc. Just as vapour or steam is formless, so also God is formless in His unmanifested or transcendental state.
 Sivananda
To achieve that state of lasting happiness and absolute peace, we must first know how to calm the mind, to concentrate and go beyond the mind. By turning the mind's concentration inward, upon the self, we can deepen that experience of perfect concentration. This is the state of Meditation.
 Sivananda
Giving is the secret of abundance.
 Sivananda