“Harvest Giving” means giving to God from the harvest, not from leftovers. After their long wilderness wandering, Moses told the Israelites always to remember all that God had done for them: hearing their cries in bondage, setting them free, leading them across a fearsome desert, bringing them to a promised land. At harvest, they were to recite their creed and then lay before God the first tenth-portion of their harvest.
Harvest giving starts in the understanding that what we have comes from God. Whether a salary, or investments, or wages, or a literal harvest of crops, the harvest comes by way of God. We, in turn, are called to give back to God a tithe (tenth portion) and to do so in profound gratitude.