Rashi: This will be "Im la'Binah Sikra" (3).

R. Yonah: After listing the attributes needed to attain Chachmah, it speaks about the benefit from it. For Chachmos such as history, geometry and Mazalos, one gets honor. For real Chachmah, one understands Yir'as Hashem, and Hashem has in His world only Yir'as Hashem (Shabbos 31b). A son fears his father, a slave fears his master, and a Talmid fears his Rebbi, to fulfill their commands, even if they know that they will not be harmed if they do not fulfill them. One who serves only due to fear of recompense and punishment, he is like one who serves his master in order to receive reward. Chazal said that we should not be like this (Avos 1:3)!

Mesilas Yesharim, introduction: It does not say 'then you will understand philosophy, astronomy, medicine, monetary laws or Halachos. Only Yir'as Hashem requires seeking it like treasure.

Malbim: "Reishis Chachmah Yir'as Hashem" (Tehilim 111:10). There is no proof for the laws of Chachmah, and they oppose the Yetzer of the heart, they can be carved into the heart only via Yir'as Hashem - 'if there is no fear, there is no Chachmah' (Avos 3:17). It says also 'if there is no Chachmah, there is no fear' (ibid.) One cannot understand Hashem's grandeur until he fears Him due to Chachmah. This teaches him to go in Hashem's ways. Via this, he understands the grandeur of the Creator, until he understands Yir'as Hashem. Via this, the laws of Chachmah will be fixed in his heart like something that he knows, even though one cannot know them via senses or proof. He will come to know exalted matters such as Ma'ase Bereishis and Ma'ase Merkavah, which we give over only to a Chacham who understands by himself.

R. Yonah: There are five levels in knowing Hashem, one above the other. (a) His existence - "v'Yadata ha'Yom va'Hashevosa El Levavecha" (Devarim 4:39), "De'u Ki Hashem Hu Elokim Hu Asanu" (Tehilim 100:3). This comes before Avodah - "Da Es Elokei Avicha v'Avdehu" (Divrei ha'Yamim I, 28:9), "Shefoch Chamasecha Al ha'Goyim Asher Lo Yeda'ucha" (Tehilim 79:6), "Yada Shor Konehu va'Chamor Evus Be'alav Yisrael Lo Yada" (Yeshayah 1:3). (b) Avodas Hashem, being careful about His Mitzvos and fearing to transgress His words. This is called knowing Hashem, for via this it is seen from man's actions that he believes in Hashem and accepts the yoke of His kingship - "Dan Din Oni v'Evyon Az Tov ha'Lo Hi ha'Da'as Osi" (Yirmeyah 22:16). (c) Knowing Hashem's ways, the Gevurah of His Chesed, His great good, contemplating His wonders, knowing His grandeur and praises, as much as man can know, contemplating Ma'ase Bereishis, Ma'ase Merkavah and words of Nevu'ah ¹ . (d) The Nefesh receives memory of Emunah in Hashem, His unity, exaltedness according to what man can understand. From this comes fundamental fear and shame that will not depart; it leads to closeness and clinging. The more one knows of His ways, the higher he can ascend. Memory is called knowing Hashem - "b'Chol Derachecha Da'ehu" (3:6); 'when you pray, know in front of Whom you pray' (Brachos 28a).

Chafetz Chaim (Toras ha'Bayis 11): It is Torah.

R. Yonah: Also this will come from Chachmah. Da'as Elokim is the perfection of Yir'ah ¹ , therefore it is put after Yir'ah, like we will explain. The Torah includes the Mitzvah of knowing Hashem in an expression of Yir'ah - "Es Hashem Elokecha Tira" (Devarim 10:20). The first matter of fear is fear of recompense and punishment in this world and the world to come. The Nefesh will receive (grasp) the matter of Hashem's grandeur, Gevurah and wonders. They will be found in the Nefesh at all times and carved into the heart. The Nefesh will receive great fear, shame and modesty at all times. It will never transgress Hashem's will, and it will be ashamed in front of Him. "Ki Pachad Elai Eid Kel umi'Seiso Lo Uchal" (Iyov 31:23) teaches about both of these. When fear comes from Yedi'as Hashem, and he knows his Nefesh's lowliness, Hashem's grandeur is always in front of him - "Shivisi Hashem l'Negdi Samid" (Tehilim 16:8), "u'Va'avor Tihyeh Yir'aso Al Peneichem l'Vilti Secheta'u" (Shemos 20:17).