Luke 10:2 (see also Matthew 9:38)
And He was saying to them, “The harvest is plentiful, but the laborers are few; therefore beseech the Lord of the harvest to send out laborers into His harvest.”
John Calvin comments: “By the metaphor, He means that many of the populace were ready to receive the Gospel.” (Calvin’s New Testament Commentaries: Matthew, Mark and Luke, Vol. I, p.278, emphasis mine)
Calvin adds: “The burden of such prayer was never greater than in the appalling devastation of the Church, as we see it everywhere today.” (Calvin’s New Testament Commentaries: Matthew, Mark and Luke, Vol. I, p.278)
Calvin also writes: “For, to stir His disciples up to diligent efforts, Christ declares that the harvest is plenteous, and therefore by implication that their labour will not be in vain but that they will find abundant opportunities for effectual work to undertake.” (Calvin’s New Testament Commentaries, A Harmony of the Gospels: Matthew, Mark and Luke, Vol. II, p.14, emphasis mine)
Calvinist, James White, writes: “God has ordained the means as well as the ends: the prayer of Luke 10:2 is that the Lord would send out workers into the harvest.” (The Potter’s Freedom, pp.264-265, emphasis mine)
In other words, God has decreed the prayers that line up with a chain of events which sees a predetermined number of “elect” people becoming saved. This matches the Calvinist mantra that prayer doesn’t change anything, but is merely a part of a predetermined chain of events.
White adds: “Obviously, this has nothing to do with with Jesus praying for unbelievers, since, of course, that would require the assumption that none of those gathered around were of the elect.” (The Potter’s Freedom, p.265, emphasis mine)