The Feasts of the Lord were seven occasions that Israel were required to rejoice before the Lord. These seven feasts were grouped into three different seasons: spring, summer, and fall. The Spring Feasts were Passover, Unleavened Bread, and Firstfruits. The Summer Feast was the Feast of Weeks. The Fall Feasts were Rosh HaShannah, Yom Kippur, and Feast of Tabernacles.
Deuteronomy 16 Modern English Version (MEV)
1 Observe the month of Aviv, and keep the Passover to the Lord your God, for in the month of Aviv the Lord your God brought you out of Egypt by night. 2 Therefore, you must sacrifice the Passover to the Lord your God, from the flock and the herd, in the place where the Lord chooses to place His name. 3 You must not eat leavened bread with it. For seven days you must eat unleavened bread, the bread of affliction, for you came out of the land of Egypt in a hurry, so that you may remember all the days of your life the day when you came out of the land of Egypt. 4 There must not be any leavened bread seen with you within all your borders for seven days, nor may any of the meat which you sacrificed in the evening on the first day remain overnight until morning. 5 You may not sacrifice the Passover within any of your gates that the Lord your God has given you. 6 But at the place where the Lord your God chooses to place His Name, there you shall sacrifice the Passover in the evening at sunset, at the time you came out of Egypt. 7 You shall roast and eat it in the place which the Lord your God will choose, and you must return in the morning, and go to your tents. 8 For six days you must eat unleavened bread, and on the seventh day there shall be a solemn assembly to the Lord your God. You must do no work on that day. 9 You shall count seven weeks for yourself. Begin counting the seven weeks from the time you begin to put the sickle to the standing grain. 10 You shall keep the Feast of Weeks to the Lord your God with a tribute of a freewill offering from your hand, which you must give to the Lord your God, in proportion to how much the Lord God has blessed you. 11 You shall rejoice before the Lord your God – you, your son, your daughter, your male servant, your female servant, the Levite who is within your gates, the foreigner, the orphan, and the widow who are among you – in the place where the Lord your God has chosen to place His name. 12 You must remember that you were a slave in Egypt, and you must be careful to observe these statutes. 13 You shall observe the Feast of Tabernacles seven days, when you have gathered in your threshing floor and your winepress, 14 and you shall rejoice in your feast, you, your son, your daughter, your male servant, your female servant, the Levite, the foreigner, the orphan, and the widow who are within your gates. 15 You are to celebrate the festival for seven days to the Lord your God in the place which the Lord will choose, because the Lord your God will bless you in all your produce, and in all the works of your hands. Therefore, you will indeed rejoice. 16 Three times a year all your males must appear before the Lord your God in the place where He will choose: at the Feast of Unleavened Bread, at the Feast of Weeks, and at the Feast of Tabernacles, and they must not appear before the Lord empty. 17 Every man must give as he is able, in proportion to the blessing of the Lord your God which He has given you.
As you can see in the above Scripture from the Word of God, there are three times that mankind is supposed to present themselves to God, especially the men. These three times are the three seasons of the Feasts of the Lord. These are stated in verse 16: the Feast of Unleavened Bread, the Feast of Weeks, and the Feast of Tabernacles.
The Feast of Unleavened Bread is in the spring season of the year. It constitutes the Feast of Passover, the Feast of Unleavened Bread, and the Feast of Firstfruits.
The Feast of Weeks is in the summer-time of the year. Christians call this Pentecost.
The Feast of Tabernacles is in the fall season of the year. It constitutes the Feast of Trumpets, Yom Kippur, and the Feast of Tabernacles.
To understand the timing of the Feasts of the Lord, one would need to now the calendar God gave Israel.
The Feasts of the Lord are a total of seven Feasts. They are a type, a figure, a picture that the people of Israel received from God. These were utilized to show Israel who their Messiah was to be and what He was to do for them and all mankind. The spring and summer Feasts have been fulfilled. The fall Feasts have yet to be accomplished.
These are the dates of the Feasts in the Jewish Calendar:
Passover (Pesach) Nisan 14-15; the first full moon of Spring
Unleavened Bread (Chag HaMotzi) Nisan 15-22
First Fruits (Yom HaBikkurim/Reishit Kaatzir) Nisan 16-17 morning after the Sabbath
Counting the Omer (Sefirat HaOmer) Nisan 16-Sivan 5
Feast of Weeks or Pentecost (Shavu’ot) Sivan 6-7
Last day of weeks sorrow Tish’ah B’Av Av 9
Rosh HaShannah or Feast of Trumpets (Yom Teru’ah) Tishri 1
Days of Awe (Aseret Y’mei Nora’im) Tishri 1-10
Day of Atonement (Yom Kippur) Tishri 10
Feast of Tabernacles (Sukkot) Tishri 15-22
The seventh day of Sukkot (HoShana Rabbah) Tishri 21
The eighth day of Sukkot (Shemini Atzeret) Tishri 22
Celebration of the giving of Torah (Simchat Torah) Tishri 23