The Forward writer Philologos in his most recent column claimed that the earliest uses of the expression והמבין יבין are found in the Ra'avad and in the Radak. Based on the fact that both these individuals lived in (late 12th century) Provence, he claims that the origin of the phrase is a Provencal translation of the New Testament. However, this expression is found earlier in the Lekach Tov (11th century Greece) and in the Ibn Ezra (early 12th c. Spain) as well as in many twelfth c. Ashkenazi works such as Rabbenu Tam's Sefer ha-Yashar, R. Yehuda b. Kalonymous' Tannaim ve-Amoraim, the Chizkuni al ha-Torah, and other places. This being the case, what is the most likely origin of the expression?
Interesting question. I'll be interested to see the response to the comments there that call the premise into question.– Seth JJun 12, 2013 at 17:07
3It seems that the original expression is המשכיל יבין, which appears in the Ibn Ezra about 20 times, and prior to that in תשובות הגאונים (presumably of Babylonian origin).– wfbJun 12, 2013 at 23:02
4@wfb: in which case it might be based on ומשכילי עם יבינו לרבים (Dan. 11:33), although there יבינו is transitive.– AlexJun 13, 2013 at 17:28
1@Alex: Interesting, & a lot more plausible for the Ibn Ezra to have had that in mind than a verse in the New Testament which means something else.– wfbJun 13, 2013 at 18:12
@wfb, I'm not sure it had to be used once originally. Although it is an "expression," it means exactly what it is used to mean.– LiquidMetalJul 21, 2014 at 22:12
Perhaps this is the source - a take off from Mishlei 19:25
לֵץ תַּכֶּה וּפֶתִי יַעְרִם, וְהוֹכִיחַ לְנָבוֹן יָבִין דָּעַת.