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 106 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.
(Baha’u’llah, Gleanings from the Writings of Baha’u’llah, p. 105)