Q. When I compared Luke 4:18-21 with Isaiah 61:1-2 I discovered it was incomplete. Why did the Lord stop reading before the end of the passage?
A. Early in His ministry the Lord stood in the synagogue in Nazareth to read the following from the scroll of Isaiah.
“The Spirit of the Lord is on me, because he has anointed me to preach good news to the poor. He has sent me to proclaim freedom for the prisoners and recovery of sight for the blind, to release the oppressed, to proclaim the year of the Lord’s favor.”
First, notice He was claiming to be the Christ, (the Greek word for “anointed” is the verb form of the word for Christ, which means “anointed one”).
Also, as you pointed out, a comparison with Isaiah 61 shows that He stopped before the end of the passage, leaving out the phrase “And the day of vengeance of our God” and all the verses following it that pertain to the Millennium.
This was a hint that because of their rejection, He would only be partially fulfilling Isaiah’s prophecy in His 1st Coming. There are several such interrupted prophecies from the Old Testament. Their ultimate fulfillment will take place in connection with His 2nd Coming.