What is the significance of "Lifnei Shever Ga'on"?
Megilah 15b: This is [one explanation] why Esther invited Haman to the party.
R. Yonah: This is next to "Shomer Nafsho Notzer Darko", for the Derech is Midos of the Nefesh. It singles out a hated Midah - pride - "To'avas Hashem Kol Gevah Lev" (5). It teaches that pride is a cause of breakage and stumbling.
Malbim: Humility and pride are both via choice. The latter elevates himself above his level. The Anav goes lowly and recognizes man's value - he should not be haughty, for he is flesh and blood. If one is proud, and rich and strong, he is prone to be broken - "Lifnei Shever Yigbah Lev Ish" (18:12). Here it says "Lifnei Shever Ga'on."
Why is Govah Ru'ach "Lifnei Chishalon"?
Malbim: Govah Ru'ach is one whose images of the Ru'ach are elevated to the heart, and they are raised to be haughty, but they were not yet carried out. The heart rules over images of the Ru'ach, and it can lower the Ru'ach, However, if [the images] affect the heart and he became Govah Lev, he is "To'avas Hashem [Kol Gevah Lev]" (5). He will be punished - "Yad l'Yad Lo Yinakeh" (ibid.) Then pride nests in his heart, and he is called haughty. If he is only Govah Ru'ach, but his heart is not yet haughty, he is close to stumbling, for pride fights with him, and he can easily stumble. After he stumbles is breakage, and then Ga'on comes first - "Lifnei Shever Ga'on." His haughty Ru'ach ruled over his heart until he came to Ga'on.
