It's the famous "cut off" point between what was written in Isaiah, and what Jesus read when he announced his arrival on the scene, in the synagogue in Nazareth.
Isaiah 61
1 The Spirit of the Lord GOD is upon me; because the LORD hath anointed me to preach good tidings unto the meek; he hath sent me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to them that are bound;
2 To proclaim the acceptable year of the LORD, and the day of vengeance of our God; to comfort all that mourn;
3 To appoint unto them that mourn in Zion, to give unto them beauty for ashes, the oil of joy for mourning, the garment of praise for the spirit of heaviness; that they might be called trees of righteousness, the planting of the LORD, that he might be glorified.
4 And they shall build the old wastes, they shall raise up the former desolations, and they shall repair the waste cities, the desolations of many generations.Luke 4
16 And he came to Nazareth, where he had been brought up: and, as his custom was, he went into the synagogue on the sabbath day, and stood up for to read.
17 And there was delivered unto him the book of the prophet Esaias. And when he had opened the book, he found the place where it was written,
18 The Spirit of the Lord is upon me, because he hath anointed me to preach the gospel to the poor; he hath sent me to heal the brokenhearted, to preach deliverance to the captives, and recovering of sight to the blind, to set at liberty them that are bruised,
19 To preach the acceptable year of the Lord.
20 And he closed the book, and he gave it again to the minister, and sat down. And the eyes of all them that were in the synagogue were fastened on him.
21 And he began to say unto them, This day is this scripture fulfilled in your ears.
The usual commentaries put the focus on the end of Jesus' earthly days -- on Palm Sunday for the big arrival scene:
Triumphal entry into Jerusalem
A group of transgender activists is planning a “Day of Vengeance” in Washington, D.C., for March 31-April 2Palm Sunday is on April 2 this year, so it looks like the two references meet up this weekend on account of the "trans" [עִבְרִי ] people.
Thought I'd make mention of it.
I thought they chose April 1 cuz they were declaring themselves fools. I shoulda known better.