Targum Yonasan: You, the Mashi'ach of Yisrael ? you are hidden due to the sins of the congregation of Tziyon. Rashi ? Migdal is an expression of strength. He translated "Eder" to be Keneses Yisrael, and Ofel with an Ayin like Ofel with an Aleph (darkness ¹ ).

Rashi: The Beis ha'Mikdash is a tower of strength. "Ofel" is like "Ofel va'Vachan" (Yeshayah 32:14). Radak ? It is a repetition of Migdal.

Radak: This is Migdal David. It is called Migdal Eder because Yisrael are compared to a flock in many places. Tziyon and Yerushalayim is the place where all of Yisrael gather three times a year, like a flock in its enclosure.

Malbim: He addresses Har Tziyon, and says 'you are the tower of this limping and cast-off flock. First you will be like a tower of flock and afterwards Ofel ? a strong fortress.

Rashi: The limping remnant and the Nahala'ah ? all of them will gather to you.

Radak: Seiseh is [coming], like u'Va'ah; the matter is repeated.

Malbim: Har Tziyon will become a strong fortress in three stages. (a) First the exiles will gather ? Yehudah and Binyamin, who are Bas Tziyon, for they were exiled from Tziyon in Churban Sheni. Refer to 4:8:3:2.

Rashi: Total authority will come to Beis David in Yerushalayim, like initially, before it was divided. It was "Mamleches l'Vas Yerushalayim." Radak ? the repetition is to strengthen the matter.

Malbim: Afterwards, the first Memshalah will come ? a small Memshalah and conduct like they had when Shoftim conducted them, before Yisrael had a king. Afterwards, Mamleches (kingship) will come to Bas Yerushalayim ? a fixed kingship, of Beis David. Afterwards Melech ha'Mashi'ach will have a fixed kingship. So it is explained in Yechezkel and Amos. Beis David will first be a judge, and rise slowly to be a kingship, until "la'Shem ha'Meluchah" in the end.