Christ, being the Paschal Lamb, had to have His Blood shed by man in atonement for man’s sins, just as the Paschal lamb under the Mosaic covenant had its blood shed by man in atonement for sin. And, just as with the Passover Lamb, the flesh had to be eaten.
You make an important note, Jesus’ New Covenant announcement and His forgiveness of sin statement (Yom Kipppur) is also combined with the sacrificial Paschal Lamb celebration commemorating Jewish Passover.
More information concerning the historical celebration by Jews of Passover:
From:
myjewishlearning.com/holidays/Jewish_Holidays/Passover/History.shtml
“Passover (Pesach) History”
"Observance of Passover has taken a number of forms through history. This evolution is partly seen in the Torah text itself. It is discussed as a springtime festival, a barley harvest festival, and a time to bring sacrifices to the Temple in Jerusalem.
Different references to Passover in the Torah as well as knowledge of other ancient rituals that took place at the same time of year indicate that there may have been several origins of the Pesach festival.
The ancient Israelites took what was originally one or more separate Canaanite spring holidays and imbued them with a heightened significance when they made Pesach a commemoration of the Exodus from Egypt.
We now view commemoration of the liberation of the Hebrews from Egyptian bondage as identical to the celebration of the Feast of Unleavened Bread.
In Leviticus (23:5-6), however, there seems to be a distinction between the two festivals.
The “Lord’s Passover” falls at dusk on the 14th day of the first month, Nisan (referred to in Torah as the month of “Aviv”).
The Festival of Unleavened Bread fell on the 15th day of the same month.
In Exodus 13:4 and Deut. 16:1, the New Moon is given as the memorial day for the Exodus.
Setting aside, slaughtering, and eating a paschal lamb was introduced as a celebration of the festival. The Hebrews were commanded to take a lamb for each household on the 10th of the first month (Nisan). The unblemished male lamb in its first year was kept until the 14th day and then killed at eve.
This ritual was reminiscent of ancient pagan rituals that took place at this time of the year. Nisan was the month when sheep gave birth and sacrifices were made at the full moon on the 15th of the month.
Passover also falls at the time of the beginning of the spring harvest.
Leviticus 23:10-16 discusses the omer [a certain measure] of new barley that was brought to the Temple on the second day of the festival.
At this time of year, the first sheaf of newly cut barley was offered up as a sacrifice. It has been suggested that the elimination of hametz (leaven), which Jews undertake before Passover, may have originated as a precaution against infecting the new crop.
Thus, Hag ha-Matzot (the feast of unleavened bread), which is a name for Passover, may have originally carried this agricultural meaning. Hag ha-Aviv, or Spring Festival, is another name for the festival of Pesach. A number of remnants of the springtime origins of Pesach remain, as in the prayer for dew, and the counting of the Omer that bridges two different spring harvest periods.
The first Pesach observance, mentioned in Numbers 9:5, took place at Sinai.
The first observance in the “holy land” is mentioned in the book of Joshua (5:10-11).
The children of Israel kept the Passover in Gilgal on the 14th of Nisan, and ate unleavened bread the next day.
It is believed that the turmoil of the Judges period that followed Joshua was not conducive to observance of Pesach.
Revival of the holiday probably occurred under Samuel in the 11th century BCE.
With the building of the Temple in Jerusalem, the observance of the festival changed.
The Temple was the focal point for the “shelosh regalim”, the Pilgrim Festivals, and it provided a place for carrying out the Pesach sacrifice. Observance of the festival waxed and waned in subsequent periods.
Historians believe that after the return from Babylonian exile and the beginning of the second Temple period, at the end of the sixth century BCE, the festival was restored to prominence.
The nature of the Pesach observance necessarily had to radically change after the destruction of the Temple in 70 CE, when animal sacrifices ceased.
A that time, Pesach was transformed from a mostly communal, public festival to one centered in the home. A Talmudic tractate devoted to the festival, Pesachim, suggests that home observance of Pesach began prior to the destruction of the Temple.
Chanting of Hallel (psalms of praise), which accompanied the slaughtering of the paschal offering began to be practiced during family feasts when the paschal lamb was eaten in private homes throughout Jerusalem."
Continues at:
myjewishlearning.com/holidays/Jewish_Holidays/Passover/History.shtml