Siman 148

(20.) (This too [was said] before the Land of Israel journey.) "The entire world needs me — not to mention you and your like, as you yourselves know. But even those tzaddikim who can already pray — I can show them that they do not know at all what prayer is, and show them a path in prayer. And also even very great tzaddikim who already walk only in yichudim [unifications] — I can show them that they do not know at all the path in yichudim, and show them a path in yichudim." And it seems he enumerated yet several more such matters.