In our passage, Paul uses the image of the firstfruits. This goes back to
Jewish festivals of Passover and Pentecost, which were both agricultural
and redemptive-historical festivals.
At the agricultural level, Passover was the time when the first crop of
barley was presented before the Lord. Firstfruits were offerings of the
produce of the land, being the first and best of the crops, given in
acknowledgment of God’s abundant blessings. Pentecost, seven weeks later,
was the time when the firstfruits of the wheat harvest were presented. It
was one of Israel’s three major agricultural festivals, the second great
feast of the Jewish year. It is a harvest festival, also known as the
Feast of Weeks.
At the level of redemptive history, Passover commemorated Israel coming
out of Egypt while Pentecost, seven weeks later, commemorated the arrival
at Sinai and the giving of Torah.
The two strands were woven together since part of God’s promise in
liberating Israel and giving it the law was that Israel would inherit the
land and that the land would be fruitful. That’s the standpoint from which
Paul is writing, and his hearers would have understood him.