John Calvin Commentary Luke 18:7

"And shall not God avenge his elect, that cry to him day and night, and [yet] he is longsuffering over them?" — Luke 18:7 (ASV)

And shall not God avenge his elect? That judge, whom Christ has described to us as utterly unprincipled—not only hardened against the thought of God but so entirely devoid of shame that he had no concern for his reputation—finally opened his eyes to the distresses of the widow. We have no reason to doubt that believers will gain at least as much from their prayers, provided they do not stop pleading earnestly with God.

Yet it must be observed that, while Christ applies the parable to his subject, he does not make God resemble a wicked and cruel judge. Instead, he points out a very different reason why those who believe in him are kept in suspense for a long time, and why he does not actually and immediately extend his hand to them: it is because he forbears. If at any time God overlooks the injuries done to us longer than we would like, let us know that this is done with a fatherly intention—to train us in patience. A temporary overlooking of crimes is very different from allowing them to remain forever unpunished.

The promise which he makes, that God will speedily avenge them, must be understood in light of his providence. For our hasty tempers and worldly understanding lead us to conclude that he does not come quickly enough to grant relief. But if we could understand his purpose, we would learn that his assistance is always ready and timely, as the situation requires, and is not delayed for a single moment, but comes at the exact time.

But it is asked, how does Christ instruct his disciples to seek vengeance, while on another occasion he exhorts them, pray for those who injure and persecute you (Matthew 5:44)? I reply: what Christ says here about vengeance does not at all conflict with his former doctrine.

God declares that he will avenge believers, not to give free rein to their fleshly desires, but to convince them that their salvation is dear and precious to him, and in this way to encourage them to rely on his protection. If, laying aside hatred, pure and free from every wicked desire for revenge, and influenced by right and well-ordered attitudes, they implore divine assistance, it will be a lawful and holy wish, and God himself will listen to it.

But as nothing is more difficult than to rid ourselves of sinful desires, if we would offer pure and sincere prayers, we must ask the Lord to guide and direct our hearts by his Spirit. Then we will lawfully call on God to be our avenger, and he will answer our prayers.