Commentaries:
The Feast of Tabernacles is different from the other festivals in that God commands that we live that week in "tabernacles" (tents), "booths" (impermanent structures), or other temporary dwellings. It is no longer required that we gather boughs of the specific trees of the Holy Land to make booths, but we do travel to another place—a Feast site arranged by the church in advance—and live in campgrounds, motels, or hotels. By this, God teaches us that, like the Israelites who lived in tents in the wilderness, Christians are pilgrims on the way to their own Promised Land, the Kingdom of God.
Of course, going away for a week or so costs money. God made provision for this in His law by commanding that we set aside a festival tithe—most often called the "second tithe"—to pay for our transportation, food, housing, and other needs during the holy days, particularly at the Feast of Tabernacles. God's instruction on this is found in Deuteronomy 14:22-26. While new Christians may see it as a burden, this second tithe is a great blessing from God, allowing us to keep and enjoy His feasts properly and to receive a foretaste of the blessings of His Kingdom.
Richard T. Ritenbaugh
How Do We Keep God's Festivals?
Deuteronomy 16:15 uses an even stronger phrase in relation to rejoicing and the feasts: "so that you [shall, KJV] surely rejoice." The wording is so strong we might be misled into thinking it is to be one big blast! Make no mistake, He desires us to rejoice, but He wants us to rejoice with purpose. If we are not rejoicing with His purpose in mind, we will have merely titillated our senses.
John W. Ritenbaugh
Preparing for the Feast
Other Forerunner Commentary entries containing Leviticus 23:40:
Leviticus 23:42-43
Deuteronomy 14:22-23
1 Kings 12:28-33