Leviticus 23 brings together the Jewish feasts including the weekly sabbath.
The sabbath was instituted at creation and became a special sign for the children of Israel (Ex 31.12-18). The Passover is strongly linked to the deliverance from Egypt. In fact, the Passover was unique in that it was only ever held once, and thereafter was a remembrance of the original celebration. This looks forward to the New Testament ‘bread and wine,’ where Christians remember the Lord Jesus giving His own life for us.
The other feasts repeat year after year, some looking back, some looking forward. Some are solemn (Atonement) some are joyful (tabernacles). The pattern of the Jewish year was built around these feasts. Interestingly, the original feasts as listed in Leviticus 23 were supplemented by Purim; see the book of Esther.
There was a further development over the generations. Luke 22.1 records that the Feast of Unleavened Bread was “called the Passover.” The two, already close, had effectively been amalgamated.
But right at the heart of this chapter in verse 22 is a reminder to remember the poor. In all their religious festivities, organising food, making sure sacrifices were suitable, etc, the slightly quaint instruction not to harvest the corners of their fields. That is for the poor. The instruction to maintain an open-handedness, and never to close their hearts to the poor, was important.