If you live to satisfy your sinful self, the harvest you will get from that will be eternal death. But if you live to please the Spirit, your harvest from the Spirit will be eternal life.
The Israelites did a foolish thing—it was like trying to plant the wind. But they will get only troubles—they will harvest a whirlwind. The grain in the fields will grow, but it will give no food. Even if it grew something, strangers would eat it.