Traditions
Worship
-Tachanun, the Prayer for
Divine Mercy
Rules
-Can delay if holiday coincides with Shabbat
-Some sects allow leeway in how close to 3
REFERENCES
1Note: Bar Yochai [Yarzeit] also called the 'godly Tanna' was the famous
Kabbalist credited as author of the Zohar. This occasion of his death is celebrated
as a festival of joy, because of his own request, noting joy of learning the Torah
as well as historical and biblical commemorations.
A Fruitful Tree
"But in the fourth year, all the fruit
therof, shall be holy to praise the LORD withalLeviticus 19
Jewish Holidays | Judah's Glory
Lag Ba'Omer, before Pentecost, is a title of a festival in the summer whose name comes from the Hebrew word
'Lag', comprised of 
the hebrew letter lamech which
stands for the number 30 and 
gimel which represents
the letter '3', hence Lag, '33' is the 33rd day of the Omer, or grain/barley harvest, preceding the
harvest of Pentecost. The event takes place on the 18th of the month Lyar. One Messianic source notes
the following:
During the days of the Tabernacle in the wilderness and during the Temple times, a sheaf, or omer, of the new barley harvest was offered to the Lord, on Nisan 16 (Leviticus 23:11). Its celebration is on the 18th day of the month of Iyyar. This offering allowed the new cereal to be eaten. After the offering, the All Mighty Lord, blessed be His name, commanded His people to “determine or count seven weeks (or seven sevens plus one day) to the day of Shavuot (meaning weeks), which falls on the 50th day. It is known in the Greek language as Pentecost, after the Greek word Penta, which means five or fifty. 1
The celebration of the holiday refers to more than just a grain offering though but also to the first farvest of fruits from trees, as the following passage indicates:
While its place among Biblical feasts is not clearly established as a major celebration,its Biblical basis is, as grain offerings at harvest are seen from as early as Cain and Abel and are prominent in firstfruits and Pentecost.This holiday is focused on Fruit and fruition and holiness, a dedication to the introduction of Torah study and becoming a child of the Commandments. The forth year, marked by the prescribed Levitical haircut, leaving the corners, represents the holiness of the child dedicated for the first time to Torah Learning, as the forth year fruit is dedicated to the LORD, that the years which follow may prosper before God. It is also referred to as the "Scholars Festival" and celebrated by attention to Jewish learning, in memory of Rabbi Yochai of Meron.And when ye have come into the land and shall have planted all manner of trees for food, then ye shall count the fruit therof as uncircumcised*: 3 years shall it be as uncircumcised unto you: it shall not be eaten of. but in the 4th year all the fruit thereof shall be holy to praise the LORD withal.
History of Lag Ba'Omer
The History of Lag Ba Omer is partly 'secular' [extra-scriptural] and partly scriptural. The Omer, a measure of grain is mentioned throught the Old Testament as are grain offerings and directives regaindg trees harvests, firstfruits and barley, but the establishment of the practice dates back to the time of Rabbi Akiva [50-135b.c.], with two stories attributed to the earliest mentions. In one, 24000 students of Akiva, were struck by a plague administered by God for disobedience, and the miraculous healing of all is said to be the celebration. In another, the 24000 were said to have been killed in the Bar Kochba revolution, and bonfires were lit in their memory, hence the tradition of celebrating learning of the Torah and lighting bonfires on that day. A student of Akiva, Rabbi Yochai, dedicated to learning and scholarship, was much revered, and is said to have written the Zohar, a premiere Kabbalist work. At his death, he requested that yearly a practice such as this be instituted in memory. Today, the traditional first haircuts are given and bonfires lit in Meron in Israel where Yochai died, and his tomb is visited. The holiday is not mournful, but a joyful day, and while observants usually take off work, it is not required as in other feasts.The firm focus on education in the Torah is central as the 3rd Birthday boys recieve their sidelocks signalling the beginning of life long torah learning. The ceremony of hair cutting is noted in historical records from the time of Rabbi Isaac Luria.
The Word of God and Lag BaOmer
While some consider this holiday an extra-biblical celebration because of its historical antecedents, the feast of Lag BaOmer is firmly rooted in the celebration of Scripture and the Law. Central passages are Leviticus 19 and 23.Whileleft the day is not counted among the major feasts of Israel, its biblical basis is clearly seen in admonitions regarding the 1)harvesting of fruit trees, 2)the harvesting, gleaning and corners of fields, and the 3) cutting of a Jewish boy/man's hair according to prescribed precepts. The celebration of the the education in Torah is certainly a biblical concepts without question. Throughout scripture as we have mentioned before, trees are often equated with the scriptures, in such passages as Psalm 1:and
Lev.....
The imagery and comparison of a tree with fruit is often used as is that of a tree prospering by waters, and so the admonition to the Jew, the believer is that we are to bear fruit nutured by living waters of the Holy Spirit. In Lag BaOmer, for the Jewish community as well as the Messianic or whole Christian community, the celebration is of Life in the Spirit and the Word. The Jews celebrate by beginning the first year of full fruit which begins following the third birthday of a Jewish child, which begins the fourth year, the year of fruit which is wholly dedicated to the LORD: with trees, so with a child's life, and as with trees the first year fruit matures, the fourth year, the apples, pears, or so forth are given to the service of the LORD often represented by alms to the poor, and the LORD is trusted to provide a healthy tree and much fruit for the life of the tree.With children, the beginning of Torah study is marked, or life in the Word. This convocation or covenant of dedication of the child in orthodoxy is marked by the first haircut leaving the corners of the hair/beard representing the corners of the field which are left. For some it is also followed by the tying on of phylacteries to mark the learning and engraving of the Word upon heart and mind. In Meron, the home of Rabbi Akiva the celebration is begun in morning prayer and celebration and the day is a day of great joy. Children play with bows and arrows, pointing to scriptures regarding the rearing of children:
As arrows [are] in the hand of a mighty man; so [are] children of the youth. Happy [is] the man that hath his quiver full of them: they shall not be ashamed, but they shall speak with the enemies in the gate. Psa 127:4-5
Celebrating Lag BaOmer
We have already mentioned several ways to celebrate Lag BaOmer: the Orthodox celebrate with visits to Meron, the traditional cutting of the sidelocks, joy and praise and readings/ prayers such as those above and the Tachanun, the Prayer for Divine Mercy, and the singing of songs such as Mi Sheberaich, a song of healing and renewal. Psalm 150 is often read. In Meron, morning prayers are said and then great parades of parents and friends go to the tomb of Akiva and bonfires are lit. In Reform and more Westernized settings, the day is often celebrated with family and synagogue picnics and sweet food and wine, and celebrations of education, and games with bows and arrows and bats and balls.Jesus and Lag BaOmer
Messianic groups are more likely to observe Lag BaOmer than Christian traditional churches, but the core of the meaning of the feast is tied to New Testament teachings as well. Continuing the great mystery of the vine of Israel and the imagery of carefully tended trees bearing fruit, it is Jesus, the husbandman of the garden who carefully and lovingly and according to the Word of God tends His beloved trees, nuturing, teaching, pruning and tithing until they bear the fruit of the Spirit. When God sends His Son looking for fruit on the tree of Israel [the fig typifies], he finds none in due season, and rebukes the tree which withers. It is on the very heels of this admonition that the Messiah walks in to take the Temple Mount which is rightfully His, to present it back holy to His Father.Likewise, it is a tree we are grafted into, the branch of Israel, the firstfruits of which are holy, and Romans 10-12 make it clear that after an anesthetizing slumber during our grafting in as gentiles, the completion of the root is grafted again in the perfection of GOD. One principle we as Christian often miss though, is that the first full year of fruit bearing is dedicated entirely to the LORD as are firstborns and tithes and firstfruits. It is said to ensure health and to cause greater fruitfullness. This is certainly a principle of the LORD, who often requires of us a first work, a first song, a first son or daughter in many ways, or another 'first' part of our lives.
Messianic concepts of the day should focus on fruit-bearing for Messiah in God's perfect order and divine plan. His fruit, not wild fruit, the way He wants it, and in the time He wishes. If we followed these principles and teachings, we would bear more and greater fruit for HIM rather than grasping and greedily holding our own plans, or coveting the plans He has for others.
He spake also this parable; A certain [man] had a fig tree planted in his vineyard; and he came and sought fruit thereon, and found none. Luk 13:7 Then said he unto the dresser of his vineyard, Behold, these three years I come seeking fruit on this fig tree, and find none: cut it down; why cumbereth it the ground? Luk 13:8 And he answering said unto him, Lord, let it alone this year also, till I shall dig about it, and dung [it]: Luk 13:9 And if it bear fruit, [well]: and if not, [then] after that thou shalt cut it down.
1IFMJ: International Federation of Messianic Jews "Counting the Omer and La Ba Omer" http://ifmj.org/articles/countingtheomer.htm