On that day I will raise up the fallen booth [i.e. sukkah] of David; I will repair their breaches and raise up its ruins, and i will build it up as in days of old so that they upon whom My Name is called may inherit the remnant of Edom and all the nations--the word of Hashem, Who shall do this (Amos 9:11-12, Stone Edition).According to Christian Scriptures (Acts 15:16), James cites this verse, albeit conjoined to entirely separate verses, in connection with their topic of the role on non-Jews in their new faith. It would seem from the line of reasoning James is presenting, as well as the general tenor of the Christian scripture's use of verses in the T'nakh, that James understood that David's booth (which had fallen but was risen) was a reference to the Messiah whom they believed to be the Nazarene. Indeed Herbert Lockyer (All the Messianic Prophecies of the Bible) understands it is such a manner (as do many other missionaries, no doubt).
Of course those familiar with the Biblical narrative immediately recognize that the "fallen booth of David" is a reference to the Davidic dynasty which ceased to reign over most of the tribes of Israel after the reign of Solomon. As highlighted by Rabbi David Kimchi 's commentary, "Since [Amos] stated the kingdom of Ephraim would fall, he now states that, in contrast, the kingdom of David would be raised up. It is symbolized by the tabernacle [sukkah] because it affords shelter to the people." (transl. by Rabbi A.J. Rosenberg, Twelve Prophets, vol. 1, Judaica Press). The Moshiach, the Messiah, is not "the fallen booth of David" but just the opposite, he is its rectification.
In line with our previous observations, this straight-forward and obvious interpretation is also the one favored by Evangelical scholars applying normal and sound exegetical principals:
David's dynasty, which had been a protective canopy over all the people of Israel, had "fallen" with the great schism o the 10 Northern tribes from the 2 Southern tribes (1 Kings 12). This booth [i.e. sukkah] had been broken in two. But God promised to unite the two kingdoms once again under Davidic rule (cf. Jer. 30:3-10; Ezek. 37:15-28; Hosea 3:4-5). He will restore the sheltering tend, repair its broken places, building it as it used to be. ( J. F. Walvoord, R. B. Zuck, The Bible Knowledge Commentary, page 1451)
While this passage is, it would seem, legitimately messianic in its meaning this does not mean that the Messiah would be "fallen". The Messianic aspect of this passage is the reversal of this fallen state. There is simply no need, nor any basis, to understand "David's fallen booth" as being the Messiah. Instead the Messiah will be the first king to reign over a united kingdom of Israel since the days of Solomon.