Perhaps when you have gone through a number of his works, or at least various parts of them, the most amazing thing, and probably the most overlooked is, like Rebbe Nachman and many of the Hassidic Rebbes, his stress on being simple and sincere with HaShem.
He totally rejects and derides philosophy (or whatever else you might call it Rationality, Intellectualism) and stresses simplicity.
Ok, fine, simple, we get the point.
But? BUT. I've never encountered a system as thoroughly complex and convoluted as that of the Kabbalah.
Try being simple and sincere while wrapping your mind around a system more complex than anything ever devised by scientist or mathematician.
The truth is you can't really make progress until you decide to experience that system spiritually, simply, sincerely, and this is what Reb Yitzhak Isaac was talking about.
People can spend a lifetime memorizing every letter combination of every name etc etc, and never touch anything true. Not so if you approach the same structure and complexity through simplicity, through sincerity.
This is the difference between relating to HaShem via Hochmah, and relating through Binah. Binah requires structures and understanding, Hochmah only works through simplicity and sincere yearning.