At an important point in The Republic, Glaucon presses Socrates on the definition of the Sovereign Good.
“But Socrates, what is your account of the Good? Is it knowledge, or pleasure, or something else?”
Socrates refuses to give an account, saying, after some further dialogue, “I am afraid it is beyond my powers; with the best will in the world, I should only disgrace myself and be laughed at.”
It is interesting to note that Dhi’lib Al-Yamani very much after the manner of Glaucon, provacatively asked the Imam whether he had seen the object of his devotion.
To this, the Imam replied, “I would not be worshipping a Lord whom I have not seen.”
Dhi’lib asked, “O Commander of the Faithful! How didst thou see Him?”
The Imam replied, “O Dhi’lib, eyes see him not through sight’s observation, but hearts see him through the verities of faith.”
This is a deep saying to meditate on. The Qur’an does refer to Ayn al-Yaqeen, the Eye of Certainty that comes with faith. I feel Imam Ali here is saying conversion is a decision of the heart, and not until an individual chooses Islam (and/or says the Shahada) does he see his Lord.