Luke 4:17-20* is the passage I was referring to. It’s an excerpt from Isaiah that was only partially read and only included His mission on earth during the first visit
18* “The Spirit of the Lord is upon Me,
Because He has anointed Me
To preach the gospel to the poor;
He has sent Me to heal the brokenhearted,
To proclaim liberty to the captives
And recovery of sight to the blind,
To set at liberty those who are oppressed;
19* To proclaim the acceptable year of the Lord.”
The passage in the Gospel according to saint Luke doesn't mention any jubilee which may be significant even if it is alluding to something like a Jubilee year.
Luke 4:16-30
16 And he went to Nazareth, where he had been raised. And he entered into the synagogue, according to his custom, on the Sabbath day. And he rose up to read.
17 And the book of the prophet Isaiah was handed to him. And as he unrolled the book, he found the place where it was written:
18 "The Spirit of the Lord is upon me; because of this, he has anointed me. He has sent me to evangelise the poor, to heal the contrite of heart, 19 to preach forgiveness to captives and sight to the blind, to release the broken into forgiveness, to preach the acceptable year of the Lord and the day of retribution."
20 And when he had rolled up the book, he returned it to the minister, and he sat down. And the eyes of everyone in the synagogue were fixed on him.
21 Then he began to say to them, "On this day, this scripture has been fulfilled in your hearing."
22 And everyone gave testimony to him. And they wondered at the words of grace that proceeded from his mouth. And they said, "Is this not the son of Joseph?"
23 And he said to them: "Certainly, you will recite to me this saying, "Physician, heal yourself." The many great things that we have heard were done in Capernaum, do here also in your own country."
24 Then he said: "Amen I say to you, that no prophet is accepted in his own country.
25 In truth, I say to you, there were many widows in the days of Elijah in Israel, when the heavens were closed for three years and six months, when a great famine had occurred throughout the entire land.
26 And to none of these was Elijah sent, except to Zarephath of Sidon, to a woman who was a widow.
27 And there were many lepers in Israel under the prophet Elisha. And none of these was cleansed, except Naaman the Syrian."
28 And all those in the synagogue, upon hearing these things, were filled with anger.
29 And they rose up and drove him beyond the city. And they brought him all the way to the edge of the mount, upon which their city had been built, so that they might thrown him down violently.
30 But passing through their midst, he went away.
While the quote from Isaiah continues
Isaiah 61:2
to proclaim the year of the Lord’s favor,
and the day of vengeance of our God;
The quote in Luke appears to be verses 1 and 2. Of course saint Luke had no verse numbers in his copy of the scroll of Isaiah nor would Jesus have had any because verse numbering didn't come into existence until the later middle ages many centuries after the gospel was written.
Isaiah 61:1-11 1 The Spirit of the Lord is upon me, for the Lord has anointed me. He has sent me to bring good news to the meek, so as to heal the contrite of heart, to preach leniency to captives and release to the confined, 2 and so to proclaim the acceptable year of the Lord and the day of vindication of our God: to console all who are mourning, 3 to take up the mourners of Zion and to give them a crown in place of ashes, an oil of joy in place of mourning, a cloak of praise in place of a spirit of grief. And there, they shall be called the strong ones of justice, the planting of the Lord, unto glorification. 4 And they will rebuild the deserted places of past ages, and they will raise up the ruins of antiquity, and they will repair the desolate cities, which had been dissipated for generation after generation. 5 And foreigners will stand up and will pasture your flocks. And the sons of sojourners will be your farmers and the workers of your vineyards. 6 But you yourselves will be called the priests of the Lord. It will be said to you, "You are the ministers of our God." You will eat from the strength of the Gentiles, and you will pride yourself on their glory. 7 Instead of your double confusion and shame, they will praise their portion. Because of this, they will possess double in their land. Everlasting joy will be for them. 8 For I am the Lord, who loves judgement and who holds hatred for robbery within a burnt offering. And I will turn their work into truth, and I will forge a perpetual covenant with them. 9 And they will know their offspring among the nations, and their progeny in the midst of the peoples. All who see them will recognise them: that these are the offspring whom the Lord has blessed. 10 I will rejoice greatly in the Lord, and my soul will exult in my God. For he has clothed me with the vestments of salvation, and he has wrapped me in the clothing of justice, like a groom arrayed with a crown, and like a bride adorned with her jewels. 11 For as the earth brings forth its seedlings and the garden produces its seeds, so will the Lord God bring forth justice and praise in the sight of all the nations.
The reference to the Jubilee referred to His mission that was to set captivity and oppression free as God had commanded during the Jubilee.
It seems there isn't an answer to why Paul would have said that.
It is not clear that either Isaiah or Luke refer to any Jubilee. The phrase "acceptable year of the Lord" is similar to the phrasing used for the jubilee year given in the law. It was one year in 50, the 49 years would pass and then the jubilee year was proclaimed.
Leviticus 25:8-22 8 You shall also number for yourselves seven weeks of years, that is, seven times seven, which together makes forty-nine years. 9 And you shall sound the trumpet in the seventh month, on the tenth day of the month, at the time of the atonement, throughout all your land. 10 And you shall sanctify the fiftieth year, and you shall proclaim a remission for all the inhabitants of your land: for the same is the Jubilee. A man shall return to his possession, and each one shall go back to his original family, 11 for it is the Jubilee and the fiftieth year. You shall not sow, and you shall not reap what grows in the field of its own accord, and you shall not gather the first-fruits of the crop, 12 due to the sanctification of the Jubilee. But you shall eat them as they present themselves. 13 In the year of the Jubilee, all shall return to their possessions. 14 When you will sell anything to your fellow citizen, or buy anything from him, do not cause your brother grief, but buy from him according to the number of years from the Jubilee, 15 and he shall sell to you according to the computation of the produce. 16 The more years that will remain after the Jubilee, the more the price shall increase, and the less the time is numbered, so much less shall the purchase price be. For he will sell to you the time for the produce. 17 Do be willing to afflict your countrymen, but let each one fear his God. For I am the Lord your God. 18 Accomplish my precepts, and observe my judgements, and complete them, so that you may be able to live in the land without any fear, 19 and so that the soil may produce its fruits for you, from which you may eat, even to fullness, dreading violence by no one. 20 But if you will say: What shall we eat in the seventh year, if we do not sow and do not gather our produce? 21 I will give my blessing to you in the sixth year, and it shall yield the produce of three years. 22 And in the eighth year you shall sow, but you shall eat from the old produce, until the ninth year, until what is new matures, you shall eat what is old.
I do not see a clear connection between the gospel according to Luke, the passage in Isaiah the prophet, and the Law in Leviticus.