The Memorial of the 1st Fruits reveals to us that Jesus Christ is the (1 Corinthians 15:20) 1st fruits of them that slept. He is the wave sheaf offering that must be accepted before the rest of the 1st fruits is accepted (Leviticus 23: 10-11).
The Feast of Harvest (also called) Feast of Pentecost, or firstfruits, teaches us that after Jesus Christ is accepted as being the 1st fruits, (the harvest) of the remainder of his elect may be accepted. The firstfruits are those who will be given salvation at the return of Christ. (James 1:18).