"He hath endowed every soul with the capacity to recognize the signs of God."

"Say: The first and foremost testimony establishing His truth is His own Self. Next to this testimony is His Revelation. For whoso faileth to recognize either the one or the other He hath established the words He hath revealed as proof of His reality and truth. This is, verily, an evidence of His tender mercy unto men. He hath endowed every soul with the capacity to recognize the signs of God. How could He, otherwise, have fulfilled His testimony unto men, if ye be of them that ponder His Cause in their hearts. He will never deal unjustly with any one, neither will He task a soul beyond its power. He, verily, is the Compassionate, the All-Merciful.

Say: So great is the glory of the Cause of God that even the blind can perceive it, how much more they whose sight is sharp, whose vision is pure. The blind, though unable to perceive the light of the sun, are, nevertheless, capable of experiencing its continual heat. The blind in heart, however, among the people of the Bayán—and to this God is My witness—are impotent, no matter how long the Sun may shine upon them, either to perceive the radiance of its glory, or to appreciate the warmth of its rays."

- Bahá'u'lláh, Gleanings From the Writings of Bahá’u’lláh, LII, pp. 105-106