The foundational claim of the sources is that fear of Heaven is not merely one virtue among many but the very gateway and root of all wisdom: Shabbat 31b compares fear of Heaven to the outer key without which even a treasurer holding all the inner keys cannot enter, and Berakhot 17a reads the pasuk 'the beginning of wisdom is fear of the Lord' as applying specifically to those who act for the Torah's own sake, warning that Torah study without this orientation leads to arrogance rather than genuine wisdom.
Mishlei itself articulates the destination of this orientation: Mishlei 2:20-22 instructs the reader to follow the way of the good and keep to the paths of the righteous, because the upright will dwell in the land while the wicked will be cut off from it — a contrast of paths whose stakes are ultimate and permanent.
The Vilna Gaon's commentary on Mishlei develops that contrast with striking imagery: Beur HaGra on Mishlei 4 describes the path of the righteous as an ever-brightening light, like dawn opening into full day, while the wicked walk in darkness and stumble without even knowing what causes their fall, their way defined precisely by the reversal and concealment of the righteous path's illumination; and Beur HaGra on Mishlei 14 extends this by explaining that the righteous person walks straight according to his own nature and fears God, whereas the wicked person perverts his path to gain human approval — substituting fear of people for fear of God.
The Malbim traces the causal mechanism by which fear of Heaven keeps a person on the righteous path: Malbim on Mishlei 8:13 argues that the first principles of wisdom cannot be reached through rational demonstration alone, and that only yirat Hashem fixes in the heart the commitment to live by wisdom's laws, while Malbim on Mishlei 4:13 adds that because the drives of the heart naturally oppose the rules of wisdom, one must grip fear of Heaven at every moment lest it slip from memory and wisdom collapse along with it.
The classical sources the Gaon drew on specify that without fear of Heaven, Torah knowledge is hollow: Nefesh HaChayim, Gate IV 4:1-3 marshals a chain of proofs — the Mishnah's 'if there is no fear there is no wisdom,' the statement in Yoma that it is woe to Torah scholars who study without fear of Heaven, and the Midrash's ruling that 'anyone who knows but has not achieved fear of sin has achieved nothing' — and Berakhot 33b grounds this in the teaching of Rabbi Chanina that everything is in Heaven's hands except fear of Heaven, the one domain of genuine human freedom.
Michtav MeEliyahu (Rav Dessler) weaves these threads together directly, citing the Gaon's reading of that same teaching from Berakhot 33b to distinguish between the lower fear — yirat tataah, the fear of sin that is the indispensable work of a person in this world — and the higher, inward fear that is ultimately a gift of Heaven; he explains that because the final telos of all creation is the attainment of that higher fear, which exceeds what human effort alone can secure, there is room to understand the divine leniency that Moshe and Eliyahu pleaded for — but this does not diminish the lower fear's necessity as the essential human initiative that makes any spiritual ascent possible.
Later authorities confirm that fear of Heaven does not merely precede wisdom but is the very condition for its endurance: Sefat Emet, Bamidbar, Shavuot 8:5 teaches that all Torah and wisdom serve only as a doorway to enter yirat Hashem, which is God's treasury, and that the one whose learning is accompanied by fear of Heaven is the one whose wisdom endures; Rav Tzadok HaKohen of Lublin similarly distinguishes between the student whose wisdom precedes fear and eventually arrives at fear — whose wisdom is then preserved — and the one who studies entirely without fear of Heaven, whom the verse calls 'a fool who pays money for wisdom though he has no heart,' placing him outside the category of wisdom altogether.
The Tanya and the Maharal supply the architectural structure underlying this whole discussion: Tanya, Part I; Likkutei Amarim 41 explains that lower fear — yirat chet — must precede wisdom as its root, and that without at least arousing this fear in the mind, even love of God cannot properly sustain the service of 'do good,' while Netivot Olam, Netiv Hatorah 1:19 adds that fear of sin is what keeps the person on the straight road directly before God without veering right or left, and that without it one cannot be said to truly walk with God at all.
