Adam Clarke on Isaiah 9:1

Dimness "Accumulated darkness" - Either מנדחה menuddechah, fem. to agree with אפלה aphelah; or אפל המנדח aphel hammenuddach, alluding perhaps to the palpable Egyptian darkness, Exo 10:21.

The land of Zebulun - Zebulun, Naphtali, Manasseh, that is, the country of Galilee all round the sea of Gennesareth, were the parts that principally suffered in the first Assyrian invasion under Tiglath-pileser; see 2Kgs 15:29; 1Chr 5:26. And they were the first that enjoyed the blessings of Christ's preaching the Gospel, and exhibiting his miraculous works among them. See Mede's Works, p. 101, and 457. This, which makes the twenty-third verse of chap. 8 in the Hebrew, is the first verse in chap. 9 in our authorized version. Bishop Lowth follows the division in the Hebrew.