This opening shot reveals two very important principles to begin our quest to find out how to keep the holy days.
The first, repeated twice in one verse, is that these festivals are God's feasts, not Israel's, not the church's. He is their Source, He set the times, He gave them meaning, and He is their ultimate Object. We could say they are all about Him—and His plan and our part in it with Him. Our observance of these days is to focus on Him and His teaching, and with that comes wonderful spiritual and physical benefits.
The second principle appears in the command to "proclaim [them] to be holy convocations." These divinely appointed times are set apart for calling together. In today's language, a primary purpose of the feasts of God is to bring God's people together, not just for fellowship, but also for instruction and most importantly, to honor and worship God Himself. These holy times, then, contain a vitally important corporate aspect, producing unity in purpose, doctrine, and relationships within the Body of Christ.
The next verse, Leviticus 23:3, presents a third important principle: "Six days shall work be done, but the seventh day is a Sabbath of solemn rest, a holy convocation. You shall do no work on it; it is the Sabbath of the LORD in all your dwellings." Along with the weekly Sabbath, the seven annual holy days—the first and last days of the Feast of Unleavened Bread (Hag Hamatzot), Pentecost (Shavuot, also called the Feast of Weeks or the Feast of Harvest), the Feast of Trumpets (Rosh Hashanah), the Day of Atonement (Yom Kippur, also called the Fast), the first day of the Feast of Tabernacles (Succoth), and the eighth day (often called the Last Great Day)—are also Sabbaths.
Like Sabbaths, they are holy convocations, as can be seen in the ensuing instructions. In most cases, the wording is that the holy day "is a holy convocation; you shall do no customary work on it" (see Leviticus 23:7-8, 21, 24-25, 35-36). This means that we are not to attend to our normal, weekday work—the kinds of activities that we do on the other six days of the week. This includes not only our paying jobs, but also the ordinary work that we would do around the house, on our cars, in our yards, at the local community center, etc.
In the instructions for keeping the Feast of Unleavened Bread, though, God stipulates, "No manner of work shall be done on them; but that which everyone must eat—that only may be prepared by you" (Exodus 12:16). Feasting is part of the holy day experience. God wants us to eat and drink of the abundance that He has bestowed upon us in thanksgiving and joy on His appointed times, so He allows us to prepare food on the holy days. Even so, it is still better to prepare as much of the food beforehand, as on a weekly Sabbath, to get the most from the feasts.
Richard T. Ritenbaugh
How Do We Keep God's Festivals?