Faith begins where knowledge leaves off, where knowledge cannot go.
If one can know something properly, there is no need to exercise faith (although what is apparent to one person may not be so to another who will have to exercise faith in order to reach the same conviction).
As Rabbi Nachman of Breslav is reputed to have said concerning the verse, "For I know that the Lord is great" (Psalms 135:5), the emphasis is on "my" knowing, on "my" being absolutely sure, and yet unable to convey this certainty.
This difference is perhaps true for all men, as implicit in the declaration "know this day and consider it in your heart."
What is prescribed here is a progression from faith to knowledge; that which one accepts as an emotionally vivid belief in the Divine has to become an intellectually clear conviction.
It is a matter of making one's faith ever more lucid and unequivocal, getting rid of the obfuscations.
Knowledge requires clarity.
As we have mentioned, almost all knowledge is quite naturally a combination of that which is sensorily perceived by oneself and of credible information received from others.
Just as on hearing a report from a traveler returning from an unknown country, one allows oneself to believe in the plausible and to entertain doubt about the rest.
The difference lies in the degree of clarity and coherence of the information, which depends also on the scope of one's previous knowledge.
But, ultimately, there always remains a certain amount of the unknown, the "mysterious."
And it is this that requires penetration and inquiry until it becomes acceptable, credible, so to speak, and is resolved into the certainty of which it is written, "And you shall know this day…. "
–Rabbi Adin Steinsaltz
From The Candle of God, p. 153, by Rabbi Adin Steinsaltz
