The word of God does not return empty or void but it waters and returns accomplishing its purposes (Isaiah 55).
We do not know when God’s purposes will be accomplished. We do not know if God’s purpose is to harden the heart or to soften it. But we ought to have absolute confidence that our work in the word is never in vain. No faithful sermon, no Bible study, no time of prayer in the word with your children, no memorizing of scripture, no ministry of the word is in vain.
Why should missionaries continue to labor in the hardest parts of the world with limited success or no success at all? Because they are confident that God has a people for himself from every tribe and language and tongue and nation, and so they stay.
Divine sovereignty—of the strong Reformed type—is one of God’s great motivators for missions. Paul says he endures all for the sake of the elect (2 Timothy 2:10). John Newton wrote a letter to Reverend Thomas Jones stating, “If I were not a Calvinist, I think I should have no more hope of success in preaching to men than in preaching to horses or cows.” Divine sovereignty should not make us lazy. It should make us long suffering.
One of the most common objections to the doctrine of election is that if it is true that God chooses who will be saved then there is not much point in working hard to get the gospel out. But this is human logic is just the opposite of biblical logic which says: if God has not chosen some to believe, then why bother speaking? Divine sovereignty in salvation is precisely the reason to keep on speaking—because God has chosen some; because God is sovereign; because God has elected; because some will believe. As Spurgeon noted, we don’t know who the elect are until they believe, so we better keep sharing the gospel, in hope and in confidence that those appointed for eternal life will believe (Acts 13:48).
God’s sovereignty is fuel for our faithfulness–not a deterrent to hard work and sacrifice, but the best motivation for it. As Luther said, reflecting on his labors for reformation: “I did nothing. The word did all the work.”