In this (path of yoga), O scion of the Kurus, there is but one-pointed determination. The thoughts of the irresolute, however, are diverse and unending. (Bhagavad Gita, 2.41)
To them, ever steadfast and serving Me with affection, I grant the yoga of understanding (buddhi yoga), by which they come to Me. (Bhagavad Gita, 10.10)
The man of steady intellect (dhira) should not swerve from his path even when oppressed by other creatures, knowing them to be under the sway of destiny; this is the lesson I have learnt from the earth. (Uddhava Gita, 2.37)
There are two signs of knowledge. First, an unshakable buddhi. No matter how many sorrows, afflictions, dangers, and obstacles one may be faced with, one’s mind does not undergo any change. It is like the blacksmith’s anvil, which receives constant blows from the hammer and still remains unshaken. And second, manliness – very strong grit. (The Gospel of Sri Ramakrishna, 410)
Take up one idea. Make that one idea your life – Think of it, dream of it, live on that idea. Let the brain, muscles, nerves, every part of your body, be full of that idea, and just leave every other idea alone. This is the way to success, and this is the way great spiritual giants are produced. (The Complete Works of Swami Vivekananda, 1.177)
As a bird flies to the sky with its two wings, so we must have the two wings of discrimination and renunciation to climb the edifice of Liberation. If one has real discrimination and renunciation, one is safe. A man runs after water in a mi rage only so long as he mistakes the mirage for real water. Once the delusion is broken, nobody goes after a mirage for water. The truth is that only he escapes whom the Mother Herself holds by the hand. Sri Ramakrishna used to say, ‘A finger print is clear when the ink is all right, and if it is bad, the impression is also bad.’ Spiritual instructions make a lasting impression only on the mind that possesses discrimination and renunciation. (Swami Turiyananda)