Rashi: He will strengthen us from two punishments that passed over us, from two Mikdashos that were destroyed. Yomayim are two eras that passed over us.

Radak: Yechayenu is a cure, like "Ad Chayosam" (Yehoshua 5:8), "va'Yimrechu Al ha'Shechin v'Yechi" (Yeshayah 38:21). If we were ill for two days, He will cure us and raise us on the third day.

Malbim: The 10 tribes were exiled three times via Sancheriv ? "ha'Rishon Hekal? veha'Acharon Hichbid" (Yeshayah 8:23). Also Shevet Yehudah was exiled three times via Nebuchadnetzar like it says in Melachim II and Yirmeyah. Therefore they request Hashem to revive them from the two days of punishment.

Rashi: It is the third era, Binyan Bayis Shelishi ? it will stand us up.

Radak: Refer to 6:2:1:2.

Radak citing Ibn Ezra: This is the opposite of anyone broken (wounded). Then, the third day hurts [most] ? "va'Yom ha'Shelishi bi'Hyosam Ko'avim" (Bereishis 34:25). Mi'Yomayim refers to the two exiles ? Egypt and Bavel, and ba'Yom ha'Shelishi is our exile. Hashem will raise us from it; we will live and never be exiled again.

Malbim: On the third Galus, they totally fell. Hashem will raise us from our fall.

Radak: We will live a long time in front of You. I.e. if our afflictions were a long time, our salvation will come soon.

Radak citing Ibn Ezra, Malbim: We will always live in front of Him and serve him ? we will not sin again.