The people which sat in darkness - This is an expression denoting great ignorance.
As in darkness or night we can see nothing, and know not where to go, so those who are ignorant of God and their duty are said to be in darkness. The instruction which removes this ignorance is called light. See John 3:19; 1-Peter 2:9; 1-John 1:5; 1-John 2:8. As ignorance is often connected with crime and vice, so darkness is sometimes used to denote sin, 1-Thessalonians 5:5; Ephesians 5:11; Luke 22:53.
Saw great light - That is, as the passage is employed by Matthew, the light under the Messiah would spring up among them. In that region he grew up, and in that region he preached a great part of his discourses and performed a great part of his miracles.
The region and shadow of death - This is a forcible and beautiful image, designed also to denote ignorance and sin. It is often used in the Bible, and is very expressive. A "shadow" is caused by an object coming between us and the sun. So the Hebrews imaged death as standing between us and the sun, and casting a long, dark, and baleful shadow abroad on the face of the nations, denoting their great ignorance, sin, and woe.. It denotes a dismal, gloomy, and dreadful shade, where death and sin reign, like the chills, damps, and horrors of the dwelling-place of the dead. See Job 10:21; Job 16:16; Job 34:22; Psalm 23:4; Jeremiah 2:6. See also the notes at Isaiah 9:2. These expressions denote that the country of Galilee was especially dark. We know that the people were proverbially ignorant and stupid. They were distinguished for a coarse, outlandish manner of speech Mark 14:70, and are represented as having been also distinguished by a general profligacy of morals and manners. It shows the great compassion of the Saviour, that he went to preach to such poor and despised sinners. Instead of seeking the rich and the learned, he chose to minister to the needy, the ignorant, and the contemned. His office is to enlighten the ignorant; his delight to guide the wandering, and to raise up those that are in the shadow of death. In doing this, Jesus set an example for all his followers. It is their duty to seek out those who are sitting in the shadow of death, and to send the gospel to them. No small part of the world is still lying in wickedness - as wicked and wretched as was the land of Zabulon and Naphthali in the time of Jesus. The Lord Jesus is able to enlighten them also, and every Christian should regard it a privilege, as well as a duty, to imitate his Saviour in this, and to be permitted to send to them the light of life. See Matthew 28:19.

The people which sat in darkness - This is quoted from Isaiah 9:2, where, instead of sitting, the prophet used the word walked. The evangelist might on purpose change the term, to point out the increased misery of the state of these persons. Sitting in darkness expresses a greater degree of intellectual blindness, than walking in darkness does. In the time of Christ's appearing, the people were in a much worse state than in the time of the prophet, which was nearly 700 years before; as, during all this period, they were growing more ignorant and sinful.
The region and shadow of death - These words are amazingly descriptive. A region of death - Death's country, where, in a peculiar manner, Death lived, reigned, and triumphed, subjecting all the people to his sway.
Shadow of death - Σκια θανατου, used only here and in Luke 1:79, but often in the Old Covenant, where the Hebrew is צל מות tsal maveth, It is not easy to enter fully into the ideal meaning of this term. As in the former clause, death is personified, so here. A shadow is that darkness cast upon a place by a body raised between it and the light or sun. Death is here represented as standing between the land above mentioned, and the light of life, or Sun of righteousness; in consequence of which, all the inhabitants were, involved in a continual cloud of intellectual darkness, misery, and sin. The heavenly sun was continually eclipsed to them, till this glorious time, when Jesus Christ, the true light, shone forth in the beauty of holiness and truth. Christ began his ministry in Galilee, and frequented this uncultivated place more than he did Jerusalem and other parts of Judea: here his preaching was peculiarly needful; and by this was the prophecy fulfilled.

The people which sat in darkness,.... The inhabitants of Galilee, who sat or "walked", as in Isaiah; that is, continued in spiritual darkness, in ignorance, blindness, error, and infidelity, "saw great light"; Christ himself, who came a light into the world; he conversed with them, preached unto them, and opened the eyes of their understandings to behold his glory, and to know him, and salvation by him.
And to them which sat in the region and shadow of death: the same persons who sit in darkness, sit also in the region of death; for such are dead in trespasses and sins: where there is no spiritual light, there is no spiritual life, and such are in danger of the second death; but the happiness of these people was, that to them "light is sprung up", like the rising sun, and this without their asking or seeking for: Christ, the sun of righteousness, arose upon them, without any desert, desire, or expectation of theirs, with healing in his wings; and cured them of their darkness and deadness, turned them from darkness to light, and caused them to pass from death to life. "Light" is not only a character under which Christ frequently goes in the New Testament, see John 1:4 but is one of the names by which the Messiah was known under the Old Testament; see Daniel 2:22 and which the Jews give unto him: says R, Aba (a) Serungia, "and the light dwelleth with him"; this is the king Messiah. The note of R. Song. Jarchi on these words, "send forth thy light", is, the king Messiah; who is compared to light, according to Psalm 132:17 the days of the Messiah are by them said to (b) be "days of light"; and so these Galilaeans found them to be; as all do, to whom the Gospel of Christ comes with power and demonstration of the Spirit. And these days of light first begun in the land of Zabulon which, according to Philo the Jew (c), was
"sumbolon fwtov, "a symbol of light"; since (adds he) its name signifies the nature of night; but, the night removing, and departing, light necessarily arises.''
As did, in a spiritual sense, here, when Christ the light arose.
(a) Bereshith Rabba, fol. 1. 3. & Echa Rabbati, fol. 50. 2. (b) Baal Hatturim in Genesis. fol. 2. 2. (c) De Somniis, p. 1113.

The people which sat in darkness saw great light; and to them which sat in the region and shadow of death light is sprung up--The prophetic strain to which these words belong commences with the seventh chapter of Isaiah, to which the sixth chapter is introductory, and goes down to the end of the twelfth chapter, which hymns the spirit of that whole strain of prophecy. It belongs to the reign of Ahaz and turns upon the combined efforts of the two neighboring kingdoms of Syria and Israel to crush Judah. In these critical circumstances Judah and her king were, by their ungodliness, provoking the Lord to sell them into the hands of their enemies. What, then, is the burden of this prophetic strain, on to the passage here quoted? First, Judah shall not, cannot perish, because IMMANUEL, the Virgin's Son, is to come forth from his loins. Next, one of the invaders shall soon perish, and the kingdoms of neither be enlarged. Further, while the Lord will be the Sanctuary of such as confide in these promises and await their fulfilment, He will drive to confusion, darkness, and despair the vast multitude of the nation who despised His oracles, and, in their anxiety and distress, betook themselves to the lying oracles of the heathen. This carries us down to the end of the eighth chapter. At the opening of the ninth chapter a sudden light is seen breaking in upon one particular part of the country, the part which was to suffer most in these wars and devastations--"the land of Zebulun, and the land of Naphtali, the way of the sea, beyond Jordan, Galilee and the Gentiles." The rest of the prophecy stretches over both the Assyrian and the Chaldean captivities and terminates in the glorious Messianic prophecy of the eleventh chapter and the choral hymn of the twelfth chapter. Well, this is the point seized on by our Evangelist. By Messiah's taking up His abode in those very regions of Galilee, and shedding His glorious light upon them, this prediction, He says, of the Evangelical prophet was now fulfilled; and if it was not thus fulfilled, we may confidently affirm it was not fulfilled in any age of the Jewish ceremony, and has received no fulfilment at all. Even the most rationalistic critics have difficulty in explaining it in any other way.

The people. Those of the region just described.
Sitting in darkness. In religious ignorance.
Saw great light. Christ, the Light of the world. In the teaching of Jesus in the region described by the prophet there was a remarkable fulfillment of the prediction.

Here is a beautiful gradation, first, they walked, then they sat in darkness, and lastly, in the region of the shadow of death.