The High Holy days are Ceremonial Laws (Holy Convocations) that the Most High required the children of Israel to observe and to keep from generation to generation forever.
The Most High instructed Israel to observe the Sabbath every seventh day, (So-called Friday sundown to so-called Saturday sundown) according to the creation account that you’re read about in (Gen. 2:1-3). The Sabbath Day is a day of rest; no work should be done on this day, (Ex 20:8-11) neither should anyone do their own pleasure on this day (Isa 58:13-14). The Sabbath was established as a covenant and a sign between the Most High and Israel, therefore breaking this law is punishable by death (Ex 31:14-17). It is a statue forever throughout your generations (Isa 66:23, Lev 23:3).
NEW MOONS SABBATH
The Most High instructed Israel to celebrate and observe the New Moon. The Hebrew month begins with the New Moon and runs for 30 days (not 31 days-read Dan. 7:25) which ends one complete cycle of the Moon. (Num 10:10, Ps 81:3-4). The Moon has four quarters to it, which make up one-month cycle (New Moon, 1st Quarter of Half Moon, Full Moon, Last Quarter Moon) and it starts with another New Moon. The Seasons and the time of Feast Days are determined by the New Moon. (Apoc. Eccles. 43:6-8). Each New Moon begins with a Sabbath and is to be observed as a Holy Convocation. (Isa 66:23) (Eze 46:13).
PASSOVER /FEAST OF UNLEAVENED BREAD
The Passover which is the Feast of Unleavened Bread (Luke 22:1) is celebrated in memory of the Most High sending his death angel through Egypt and killing all the first born of the Egyptians, and passing over the House of Israel in Egypt. (Ex 12:26-27) the Passover which is the Feast of Unleavened Bread comes on the 14th day of the First month at sundown, which is the beginning of the 15th of April. It is observed for seven days by eating Lamb, which is sacrificed and roasted just before sunset on the 14th day; Unleavened bread which is a symbol of purity and cleaning, and bitter herbs which represented the bitterness of the bondage in Egypt. (Ex 12:1-18) Unleavened Bread should be eaten for seven days. The first day is a Sabbath and the seventh day is a Sabbath. It is a Holy Convocation throughout your generations. (Deut 16:1-8).
FEAST OF FIRST FRUITS
(Lev 23:10-16) The celebration of First Fruits (same as Feast of Weeks or Pentecost). It marks the beginning of the harvest (barley) and seasonal offering of First Fruits to the Most High. (Deut 16:9-12) The wave offering begins the morrow after the Sabbath after the Feast of Unleavened Bread (Passover) of the First Month (Abib). The morrow after the Sabbath is Sunday. The Sabbath is Saturday the 7th Day. From the day that ye bring the wave offering, count seven Sabbaths and after the morrow after the seventh Sabbath shall ye number 50 days. The 50 days falls on a Sunday; this is the day of Pentecost – which means fifty. It is observed with a Sabbath and is a Holy Convocation. (Num 28:26)
MEMORIAL OF BLOWING TRUMPETS
(Lev 23:24-25) The Memorial of Blowing Trumpets, came on the 1st Day Seventh month, and is celebrated by the Priest blowing the trumpets, (Num 10:8) to mark the end of the harvest season. And all the blessing the Most High gave to Israel throughout the year in their crops. Also, the New Moon is commemorated on this day and is observed as a Sabbath day a Holy Convocation throughout your generations. (Psa 81:3-4).
DAY OF ATONEMENT
(Lev 23:27-32) The Most High required the Israelites to fast or afflict your souls, once a year to make an atonement for their sins they had committed the whole year. Atonement - (To reconcile or make amends) the Priest in Israel would make Atonement for the nation once a year. To cleanse their sins before The Most High. (Lev 16:29-30) The Day of Atonement is observed on the Seventh month 10th day by having a Sabbath and every soul must be afflicted (Fast). It is a Holy Convocation throughout your generations.
FEAST OF TABERNACLES
(Lev 23:34-44) The Most High required Israel to have celebration to commemorate their wandering in the wilderness for forty years. First, it is a celebration of the end of harvest seasons or ingathering, and blessings of a fruitful season. (Ex 23:14-16) Secondly, the people of Israel were required by The Most High to dwell in booths made out of boughs of trees and branches of palm trees, to commemorate our dwelling in booths in the wilderness. Feast of Tabernacles begins on the 15th day of the Seventh month to the 22nd day, and goes for eight days. First day is a Sabbath and the last day is a Sabbath. It is a Holy Convocation throughout your generations. (Deut 16:13-15)
HANUKKAH/FEAST OF LIGHTS
Hanukkah - (to dedicate) in 168 BC Jerusalem the Temple was plundered and destroyed by the Greeks und Antiochus IV. Under the military leadership of Judas Maccabeus in 165 BC. The city and The Temple were taken back and re-established. The Temple was repaired and dedicated (John 10:22) to The Most High for the victory over the Greeks. The Jews under Judas Maccabeus ordained that the days of dedication would be kept for eights days from the 25th of the Ninth month to 3rd day of the Tenth month. (Apocrypha II Maccabeus 4:52-59) It is marked by the lighting of eight candles one on each day of the feast. The First Day is a Sabbath; it is a Holy Convocation throughout your generations.
Purim (To cast lots) this Feast Commemorated the Jews deliverance from Haman while they were in captivity under Persian rule. Haman (Edomite so-called white man) was promoted in rank under King Ahasuerus, when Mordecai, Queen Ester uncle did not bow to him, Hanman sought to destroy all the Jews, by casting Pur; that is, the lot. Mordecai convinced Queen Easter to go before King Ahasuersu, to persuade him that Haman is wicked and an enemy to the Jews. King Ahasuerus had Haman and his sons hanged, and the Jews were delivered from that wicked plot of Haman. Therefore, Purim is celebrated on the 14th and 15th day fo the twelfth month and begins with a Sabbath. It is a Holy Convocation throughout your generations. (Ester 9th Ch)