The feasts of Israel are those described in Lev 23. The three pilgrimage feasts—the Passover, the Feast of Weeks, and the Feast of Tabernacles—demanded that every male Israelite travel to Jerusalem to worship at the temple. The Passover and the Feast of Unleavened Bread are closely related and ran consecutively (Lev 23:4–8). The Feast of Weeks (Pentecost) followed seven weeks later, and connected the Passover of the exodus with the bounty of the conquest. Both Passover and Pentecost are practiced by early Christians—Christ was crucified at the Passover, and the Holy Spirit personally descended upon the disciples on Pentecost (Acts 2). The Bible ends with the anticipation of one final feast: the Marriage Supper of the Lamb (Rev 19:9).
Because Jesus fulfilled the Spring feasts: Passover-Pentecost with his death burial, resurrection, ascension and subsequent outpouring of the Holy Spirit. This leads many to suspect the Fall feasts: (Trumpets, Day of Atonement, Tabernacles) are connected to his second coming. This is somewhat compelling but not necessary. God nowhere promised that Jesus would return on a certain feast day and certainly never implied that observing them is required to be found in good stead when he returns.
While the feats of the Lord are interesting for prophetic study, some have wandered away from biblical theology by implying new covenant believers are required to observe the Mosaic laws regarding feast observance. This error was dealt with by Paul when false teachers in Colasse:
“I say this in order that no one may delude you with plausible arguments. For though I am absent in body, yet I am with you in spirit, rejoicing to see your good order and the firmness of your faith in Christ. Therefore, as you received Christ Jesus the Lord, so walk in him, rooted and built up in him and established in the faith, just as you were taught, abounding in thanksgiving. See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirits of the world, and not according to Christ.”(Col 2:4–8)
This is exactly what is re-occuring in our own context with false teachers who are putting folks back under the obsolete law by implying that feast observance is needed for spiritual advancement and sanctification. Paul addressed the feats specifically:
“Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath.” (Col 2:16)
Paul was addressing the false teacher(s) in Colasse who were advocating a number of Jewish observances, arguing that they were essential for spiritual advancement.
“These are a shadow of the things to come, but the substance belongs to Christ.”(Col 2:17)
The old covenant feast observances pointed to a future reality fulfilled in the Lord Jesus Christ (cf. Heb. 10:1). Hence, Christians are no longer under the Mosaic covenant (cf. Rom. 6:14–15; 7:1–6; 2 Cor. 3:4–18; Gal. 3:15–4:7). Christians are no longer obligated to observe OT dietary laws (“food and drink”) or festivals, holidays, and special days (“a festival … new moon … Sabbath,” Col. 2:16), for what these things foreshadowed is fulfilled in Christ.
Hebrews 8-10 explains very clearly that Christ’s atoning death on the cross was the end of the law and it is now obsolete for everyone. “In speaking of a new covenant, he makes the first one obsolete. And what is becoming obsolete and growing old is ready to vanish away.”(Heb 8:13)