Why is it 'firstfruits' plural instead of 'firstfruit' singular in 1 Corinthians 15?
It is plural because the firstfruits include more than Christ alone. Christ is the first resurrected, but the Jewish saints raised immediately after Him join Him as the sheaf of firstfruits. Leviticus's feast required many grain stems, not one, so together they complete the plural word firstfruits.
Les explains that Christ was the first to be resurrected from the dead, but He did not come alone. After His resurrection, others came forth and together comprised the sheaf indicated in Leviticus, completing the plural word “firstfruits.” Had Christ only come alone, He would have to be called the firstfruit singular. But the feast day of firstfruits took not just one stem of grain; it took many, all sampling the crop to come. They were brought together in a sheaf and taken to the priest as the offering of firstfruits. So these Jewish saints resurrected right after Christ comprise what is called the firstfruits. Les also notes that church age saints will not be part of the firstfruits, because that has already happened, and resurrection occurs within companies, as 1 Corinthians 15:23 indicates.