Above (verse 23), he said that they will be wood choppers and water drawers for Beis Hashem. Why did he say here that they will do so for the congregation and the Mizbe'ach?
Malbim: Beis Hashem (the Mishkan) was not in its place. Until it is established, they will be wood choppers and water drawers for the congregation engaged in war during the seven years of conquest and seven of division. After that, they will cut wood for Mizbach Hashem.
Perhaps here it means that forever, Yisrael may force Giv'onim to chop wood and draw water for Beis Hashem, if it exists, or for the congregation. Alternatively, "Ad ha'Yom ha'Zeh" is not always forever. It says "va'Yhi Sham (the Aron was in the Mikdash] Ad ha'Yom ha'Zeh" (Divrei ha'Yamim 2 5:9). This is difficult even if "Ad ha'Yom ha'Zeh" means until this verse was written (after the Churban)! Metzudas David explains there, until the Aron was hidden. (PF)
What is the meaning of "Ad ha'Yom ha'Zeh"?
Rashi (Bereishis 22:14): Whenever it says so in Tanach, it is [forever], whenever someone will read the verse. 1
Malbim: It is the day that Sefer Yehoshua was written.
What is the meaning of "El ha'Makom Asher Yivchar"?
Malbim: It is at the time Hashem will choose a place to dwell. (Then, they will serve only the Mizbe'ach.)
