Proverbs 3:9-10
   Honour the Lord with thy substance, and with the firstfruits of all thine increase: So shall thy barns be filled with plenty, and thy presses shall burst out with new wine.

   At the first increase acknowledgment of God as our provider is vitally important. Whenever we are blessed by God we should respond by giving back to God the firstfruits. God promises that when we give he will respond with plenty.

   In the Old Testament God set up three required feasts for the Children of Israel. These are outlined in Exodus:

Exodus 23:14-17
   Three times thou shalt keep a feast unto me in the year.
   Thou shalt keep the feast of unleavened bread: [Passover] (thou shalt eat unleavened bread seven days, as I commanded thee, in the time appointed of the month Abib; for in it thou camest out from Egypt: and none shall appear before me empty:)
   And the feast of harvest, the firstfruits of thy labours, which thou hast sown in the field: and the feast of ingathering, which is in the end of the year, when thou hast gathered in thy labours out of the field.
   Three times in the year all thy males shall appear before the Lord God.

   The "feast of harvest" was the second feast. It was a time for Israel to acknowledge God with the firstfruits of the harvest. It will be seen that this feast is also called "the feast of weeks", and in the new testament: "Pentecost."

Exodus 34:22
   And thou shalt observe the feast of weeks, of the firstfruits of wheat harvest, and the feast of ingathering at the year's end.

   The timing of the feast of harvest [Pentecost] was determined by counting seven weeks after the wave offering presented by the priest on the first day of the week following the weekly sabbath at the feast of Passover. Therefore it was called "the feast of weeks."

Leviticus 23:10-12
   Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of the firstfruits of your harvest unto the priest:
   And he shall wave the sheaf before the Lord, to be accepted for you: on the morrow after the sabbath the priest shall wave it.
   And ye shall offer that day when ye wave the sheaf an he lamb without blemish of the first year for a burnt offering unto the Lord.

   The day after the weekly sabbath during the feast of Passover the priest would present the wave offering and a lamb of the first year before the Lord. In the year that Jesus Christ was crucified and raised from the dead he was both the offering of the lamb and the high priest that offered. On the first day of the week [Sunday] after the sabbath this offering was to be presented to the Lord. When Jesus Christ met Mary early that morning [John 20:17-18] he told her not to touch him for he "had not yet ascended to his Father." Later that same day he told the apostles to touch him. Early that morning he entered the Temple as the high priest and presented himself as the firstfruits from the dead.

1 Corinthians 15:20-23
   But now is Christ risen from the dead, and become the firstfruits of them that slept.
   For since by man came death, by man came also the resurrection of the dead.
   For as in Adam all die, even so in Christ shall all be made alive.
   But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming.

   The feast of weeks, feast of harvest, Pentecost was determined by counting seven weeks from the presentation of the wave offering.

Leviticus 23:15-16
   And ye shall count unto you from the morrow after the sabbath, from the day that ye brought the sheaf of the wave offering; seven sabbaths shall be complete:
   Even unto the morrow after the seventh sabbath shall ye number fifty days; and ye shall offer a new meat offering unto the Lord.

   The term "Pentecost" is derived from the number 50. Seven weeks (49 days) plus one day were counted to determine "the feast of weeks." The weeks were numbered from the day of the wave offering which was a presentation of the firstfruits of the harvest.

Deuteronomy 16:9-11
   Seven weeks shalt thou number unto thee: begin to number the seven weeks from such time as thou beginnest to put the sickle to the corn.
   And thou shalt keep the feast of weeks unto the Lord thy God with a tribute of a freewill offering of thine hand, which thou shalt give unto the Lord thy God, according as the Lord thy God hath blessed thee:
   And thou shalt rejoice before the Lord thy God, thou, and thy son, and thy daughter, and thy manservant, and thy maidservant, and the Levite that is within thy gates, and the stranger, and the fatherless, and the widow, that are among you, in the place which the Lord thy God hath chosen to place his name there.

   All came to celebrate the feast of weeks, Pentecost, in the place which the Lord hath chosen to place his name. In the time of Jesus Christ this was the Temple in Jerusalem.

John 4:19-24
   The woman saith unto him [Jesus], Sir, I perceive that thou art a prophet.
   Our fathers worshipped in this mountain; and ye say, that in Jerusalem is the place where men ought to worship.
   Jesus saith unto her, Woman, believe me, the hour cometh, when ye shall neither in this mountain, nor yet at Jerusalem, worship the Father.
   Ye worship ye know not what: we know what we worship: for salvation is of the Jews.
   But the hour cometh, and now is [almost here], when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him.
   God is a Spirit: and they that worship him must worship him in spirit and in truth.

   The place that God chose to place His name was the Temple in Jerusalem. But Jesus told this woman that a day was coming that the true worshippers would offer true spiritual worship and that God would be present via spirit in each individual believer. God would bless all with the gift of holy spirit and man would be able to offer the firstfruits of true worship via speaking in tongues.

Acts 2:1-11
   And when the day of Pentecost was fully come, they were all with one accord in one place.
   And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting.
   And there appeared unto them cloven tongues like as of fire, and it sat upon each of them.
   And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
   And there were dwelling [for the feast of weeks] at Jerusalem Jews, devout men, out of every nation under heaven.
   Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.
   And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?
   And how hear we every man in our own tongue, wherein we were born?
   Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,
   Phrigia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes,
   Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.

Romans 8:23
   And not only they, but ourselves also, which have the firstfruits of the Spirit, ...

James 1:17-18
   Every good gift [offering] and every perfect gift [act of giving] is from above, and cometh down from the Father of lights, which whom is no variableness, neither shadow of turning.
   Of his own will begat he us with the word of truth, that we should be a kind of firstfruits of his creatures.

   We are the firstfruits of God. We have been given holy spirit and we can offer back to God true spiritual worship via speaking in tongues.