The passage about the gospel in Luke 4 is breathtaking; in some ways it sums up and carries through everything Jesus says about “gospel.” But there are other texts that need to be discussed as we ponder the meaning of “gospel” in a world obsessed with truncating it to one or two or three or four simple ideas.
The next text builds directly on Luke 4 but extends it because it moves beyond Isa 61, which was the text behind Luke 4. That text is Luke 7:18-23:

18 John’s disciples told him about all these things. Calling two of them, 19 he sent them to the Lord to ask, ?Are you the one who was to come, or should we expect someone else?? 20 When the men came to Jesus, they said, ?John the Baptist sent us to you to ask, ?Are you the one who was to come, or should we expect someone else?? ?
21 At that very time Jesus cured many who had diseases, sicknesses and evil spirits, and gave sight to many who were blind. 22 So he replied to the messengers, ?Go back and report to John what you have seen and heard: The blind receive sight, the lame walk, those who have leprosy are cured, the deaf hear, the dead are raised, and the good news is preached to the poor. 23 Blessed is the man who does not fall away on account of me.?

First, Jesus is in the middle of it: John wants to know if Jesus is the “one who is to come”, which could refer to “Messiah” (in which case Jesus says indirectly “yes” to the question) or to the figure of Malachi 3–4 (in which case Jesus indirectly “no, tell John he is; I’m someone else”). And v. 23 makes himself the middle of it all.
Second, Jesus appeals here to Isa 29, Isa 35, and to Isa 61 when he lists what it is that reveals who he is and what his gospel is. He’s God’s Agent of the Kingdom.
Third, the gospel — good news — is for the poor. The poor, the marginalized, are the ones at whom Jesus directs his gospel. This could be “inclusive” — his good news doesn’t exclude the poor but includes them — or this could be a massive warning — his good news is aimed at the poor — and in this case “poor” probably includes each of the people/sick groups mentioned in v. 22.