Holidays such as Christmas, Easter, Lent and Halloween are deeply ingrained into the tradition of our culture. These holidays are much loved and are associated with dear memories. For these reasons it's very difficult for us to look at them in light of God's Word.
     My purpose here is not to explore the origins of the holidays, except to say that early on the Roman Catholic Church adopted pagan practices and "transformed" them into Christian holidays. Proof of this can easily be found in encyclopedias, libraries or on the internet.
     Many people think their motives justify celebrating these holidays. They claim that they are "redeeming" the holiday for the Lord. These holidays were never the Lord's to begin with so how can sinful man "redeem" something God wants nothing to do with? Many attach "Christian" symbols to the pagan traditions associated with these holidays. They are sadly and foolishly trying to justify what is abhorred by God.  It's not easy to give up our much loved holidays, but they become an increasing burden as one applies Scripture to them. How much more satisfying to please the Lord in the way He has prescribed.
     The best place to begin studying God's feasts is at the beginning in Gen.1:14: "And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years." The word "seasons" means: appointment, fixed time, solemn assembly, a signal as appointed beforehand. The same Hebrew word is used in Lev.23:2,4. Feasts is mentioned  3 times and seasons once in these verses. "Feasts" is the same word in the Hebrew as the word for "seasons" in Gen.1:14.  Psalm 104:19, 148:6 and Jer.31:35,36 verify God's use and the enduring function of the heavenly lights. God says in Lev.23 that these are "feasts of the Lord," "holy convocations," "My feasts." They are ordained by God. They are not manmade as are our "holidays." God established other commands or ordinances at creation as well, such as marriage, being fruitful and muliplying, man's dominion over the earth, and the 7th day Sabbath.
     God's feasts are to be kept for "ever." This word means: time out of mind, eternity, always, eternal, perpetual.  In Ex.12 the Passover and Feast of Unleavened Bread were instituted. It was to be kept as "a feast by an ordinance(appointment) for ever." Lev. 23 restates the Passover and Feast of Unleavened Bread. We also see the Feast of Weeks or Pentecost to be kept "forever," v.14, and the Feast of Trumpets and The Day of Atonement to be kept "forever," v.31, and finally the Feast of Tabernacles to be kept "forever," v.41.
     Scripture goes on to show us that God's feasts will be kept in the millennium or new heavens and new earth.  According to various sources, Eze.45:17-25 shows the new moon, Passover, Unleavened Bread and the Day of Atonement being kept at that time. Then in Zech. 14:16, the Feast of Tabernacles is still being kept and in Isa.66:22,23, we see the new moon and Sabbath being kept.
     You may be thinking all of that is in the Old Testament. What about the New Testament? In the gospels Christ Jesus obeyed all His Father's commandments. He stated that if we loved Him, we too would keep them. The gospel of John gives the most examples: 2:13,23;  5:1;  6:4;  7;  13:1; 14:15,21,23; 15:10; 1 John 3:22,24; 5:2,3. Then in the Book of Acts, the disciples continue in obedience to God's word: 2:1; 12:3; 18:21; 20:6,16. Also look at I Cor.5:7,8; 16:8 and Rev.19:9. God's word continues in its validity: "Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfill. For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled. Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven." "Heaven and earth shall pass away: but My words shall not pass away." Matt.5:17-19 and Mark 14:31 .
     Some may think these feasts are for the Jews only, but God even made provision for the stranger or sojourner among His people. One of many examples is found in Num. 15:15,16: "One ordinance shall be both for you of the congregation, and also for the stranger that sojourneth with you, an ordinance for ever in your generations: as ye are, so shall the stranger be before the Lord. One law and one manner shall be for you, and for the stranger that sojourneth with you." God's people are more than just the Jewish believers  In Eze.11,36, and Jer.31, the New Covenant is stated: "A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you a heart of flesh. And I will put My Spirit within you, and cause you to walk in my statutes, and ye shall keep My judgments, and do them." Eze.36:26,27.  It is then repeated in Heb. 8 and 10.  A new "administration" of the law - the Holy Spirit through Christ Jesus is now in effect. Believers are called strangers, pilgrims, peculiar people, a chosen generation, etc. This is consistent through out the Bible: Deut.7:6, Ps.119:19, Heb.11:13, 1 Pet.2:9,11. Galatians 3:28,29 states it beautifully: "There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise." 
      Another very interesting and important aspect about God's Holy days is that they are memorials of great events and/or point to great future events. And the more you study them, the more your eyes are opened to the rich fulness of their meanings. I'd like to touch on a little of this. Starting with Passover/Unleavened Bread, we see it is a reminder of God's deliverance of the Israelites from slavery in Egypt. This pictures a believers slavery to sin. The sacrificial lamb protected the people from the death plague - in like manner Jesus, our sacrificial Lamb, saves us from the death penalty of sin. And the leavening represents sin, so the people were not to eat any leavened foods for this period of time. They were to remove all leavening from their household. How hard it was to be completely thorough. How hard and impossible it is to keep from sinning in some way for any length of time. Removal of the leavening was a physical way to help understand the pervasiveness of our sin nature. (Scripture references: Ex.6:6,7; 12; 13:3-10; Lev.23:4-5; Num.28:17-25; Gen.22:1-13; Isa.52:13-15; 53; Matt.26:17-29; Acts 20:6; I Cor.5:6-8; 11:26-29)
     The holy day of First Fruits is celebrated on the day after the first sabbath  that comes after Passover(which would be a Sunday- and is typically the day when "Easter" is celebrated!). This day looked forward to the resurrection of Jesus. He is the First Fruit of those believers whom He will someday raise from the dead. Now what need do we have to celebrate "Good Friday" or "Easter" when Passover/Unleavened Bread and First Fruits are the memorials and actual pictures of why Christ died for us? (Scripture references: Lev.23:10-14; Acts 26:23; I Cor.15:20,23; Col.1:18; Jm.1:18; Rev.1:5; 14:4)
     Then there is Pentecost, also called the Feast of Weeks because it is celebrated 7 weeks after Passover. In the New Testament book of Acts we see the giving of the Holy Spirit to the new church at this time. This is also a memorial of when God gave His law, the 10 commandments, to the Israelites after He brought them out of Egypt. In like manner the Holy Spirit was given under the New Covenant to write God's laws in our hearts. (Scripture references: Ex.23:16; 34:22,26; Lev.23:1-21; Num.15:15-21; 28:26; Deut.16:9-15; Jer.31:33; Acts 2; 20:16; I Cor.16:8; Heb.8:10; 10:15,16.)
     The Feast of Trumpets was a reminder to be ready for God's signal. In old times the trumpet was used to announce something. The people were to be alert and ready to respond. Trumpets will be used again in the future at the return of Jesus and we too must be listening and ready and looking for His return. (Scripture references: Lev. 23:24,25; 25:9; Num. 10:2,4,10; 29:1-6;  I Sam.13:3,4; II Sam.15:10; I Kings 1:34; II Kings 9:13; Jer.4:5; Joel 2:15,16; II Chr.7:6; Zech.9:14; Isa.18:3; Zeph.1:14-16; Matt. 24:31; I Cor.15:51,52; I Thess.4:16; Rev.8; 9.)
     The Day of Atonement is a time to remember what it took for God to redeem us. It is a time to reflect on what we are in our sinful state to the eyes of our most Holy God. We must never take for granted the tremendous cost that was paid to redeem each one of us. This feast looks forward to when Christ will bring His ransomed church into the presence of the Father to be made at-one with Him. (Scripture references: Lev.16:29-34; 23:27-32; Isa.58; Ps.51:2; Heb.7:15-17; 9; Eph.5:25,26; I Jn.1:7.9)
     And last is the Feast of Tabernacles, which takes place in October and has multiple meanings. It was to remind the Israelites of the time they spent in the wilderness - they were pilgrims and strangers and the earth is only a temporary dwelling. Another wonderful meaning of the Feast of Tabernacles is that it is the time of "ingathering." The fall crops are harvested. This pictures the time when Christ returns and gathers His people to Himself. And one of the most special pictures is that it pointed to the time when Christ was to be born.  Jn 1:14 says: "The Word became Flesh and dwelt among them."  Tabernacle means "dwelling."  Jesus literally dwelled with man on earth for a time.  And now, God, through His Holy Spirit, tabernacles or dwells in the believer. Though the Bible gives no specific time for Christ's birth, I am convinced God would choose no other timetable than that which He had set up in His Holy Days. From the Gospel of Luke, a very good study has been made of the time when Elisabeth, Zacharias' wife, became pregnant. He was serving his priestly duties in the temple during the "course of Abia". And only  6 months later, Mary became pregnant. To learn more about this, you might want to read these articles:
http://www.aloha.net/~mikesch/sukkoth.htm        
http://www.circlegame.com/live/birth.htm

     Jesus is NOT "the reason for the season."  It is foolish to "keep Christ in Christmas" when December was not the time of His birth, and was a man instituted holiday anyway. We think we honor Jesus by celebrating His birth, but is it honoring to do so  2 months after the fact, and at a time that was not part of God's holy plan?  People will say that many of the unsaved are reached at that time of year. It is true that God can and does touch peoples' lives at that time of year. But how much more effective and powerful would the Christian's witness be if we celebrated the birth of Christ when it actually happened and in accord with God's word?!!!! I think we are missing a tremendous opportunity to see the fullness of God at work because we are compromising His word. (Scripture references: Lev.16:2; 23:34-44; Ex.23:16; 25:22; 29:42-46; 33:7-14; 40:34,35; Num.17:4; Deut.16:13-15; I Kings 8:10-12; Ezra3:4,5; Neh.8:14-18; Jer. 7:18, 10:1-4, 44:15-19; Zech.14:16; Hos.12:9; Jn.7:2,37; 14:17; II Cor.6:16; I Jn.2:27; Rev.21:3)
     There are those who use Gal.4:9-11, Col.2:16, and Rom 14:5 to justify their "freedom" in celebrating holidays. But do you really think the apostle Paul wrote these verses in order to give people license to celebrate clearly pagan holidays, which are forbidden to God's people?  If we came from the mindset of keeping God's holy days, these verses would make perfect sense. Coming from the mindset of our day - the celebrating of "holidays", which weren't even invented yet,  makes these verses a stumbling block. Christians have spent the last 2000 years trying to divorce the Old and New Testaments. No wonder we have so much trouble unraveling our current understanding towards God's holy days.
     We must take the word of God seriously for we are forbidden to have anything to do with paganism: "Take heed to thyself that thou be not snared by following them, after that they be destroyed from before thee; and that thou inquire not after their gods, saying, how did these nations serve their gods? even so will I do likewise. Thou shalt not do so unto the Lord thy God: for every abomination to the Lord, which He hateth, have they done unto their gods; for even their sons and their daughters they have burnt in the fire to their gods. What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it." Deut.12:30-32. The New Testement reiterates the same warning in II Cor.6:14-18: "Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness? And what concord hath Christ with Belial or what part hath he that believeth with an infidel? And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be My people. Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you, and will be a Father unto you, and ye shall be My sons and daughters, saith the Lord Almighty." We are also forbidden to add or to change God's Word (see Deut.4:1-20; Prov.30:5,6 and Rev.22:18). The addition of "holidays" in the name of God is adding to His word.
     As a quick review, here are the reasons I believe that God's holy days are still valid:
1. The heavenly light were established at creation to notify us of God's
    scheduled holy days.
2. The Bible shows us that the holy days belong to God, they are "My feasts."
3. The Bible repeatedly states that the feasts are to be kept forever.
4. The Bible shows that God's feasts will be kept in the new heavens and new earth.
5. The feasts were kept by Jesus and the apostles.
6. The holy days are to be kept by God's people. All true believers are God's people.
7. We are forbidden to have any association with paganism.
8. Whether one literally celebrates the holy days or not, they all have spiritual application and
    manifestation in each believer's life.

     It takes some time to adapt to new ideas and make the appropriate changes, but the spiritual blessings in pleasing our Heavenly Father are more than ample reward.