Why does it say "Yashuvu Al Ekev Bashtam"?
Rashi (here and 40:16): This is Midah k'Neged Midah. They will be shamed in the full Midah that they meted out and in the way they came against me. "Al Ekev" is on the same path, like "v'Ikevosecha Lo Noda'u" (77:20), "Tze'i Lach b'Ikvei ha'Tzon" (Shir ha'Shirim 1:8).
Radak: They will be turned back as 'payment' for the shame that they shamed me at the time of my affliction, and be shamed, Midah k'Neged Midah. Ekev is reward, like "Ekev Tishme'un" (Devarim 7:12).
Malbim: Those who falsely slandered me and testified about evil that they saw in me, their shame [that they caused me] will come back upon them.
Why do they say "He'ach"?
Rashi: It is an expression of Simchah, when they see him in his enemy's [hand], as they wanted.
Radak: So they said when I fled - Simchah, Simchah! Radak (40:15) - we find "He'ach He'ach Ra'asah Einenu" (35:21).
