Because God will answer our cries with justice, we are to persevere through prayer.
Scripture tells the sad stories about people who once lived by faith but gave up. Paul recounts some of them. One, in particular, named Demas, seemed to trouble Paul the most (2 Timothy 4:10). Demas was condemned for desertion, leaving Paul and his companions during a moment of need.
"Giving up" is a common occurrence when we lose sight of our end goal. We give up exercise routines when we don't feel the weight loss that we expected; we give up relationships when we discover they are harder to maintain than we wanted; we give up jobs when we feel undervalued and underappreciated; we give up on churches when church leaders disagree with us; and we give up on spiritual practices like prayer when we don't get the answers we want.
At the root of giving up is the recognition that our expectations are separated from our reality. What we thought would happen didn't happen, so we simply give up. We lose heart. We lose faith.
Not all giving up happens quickly. Sometimes it does. Sometimes a person will start a new exercise routine and quickly realize this particular mode of exercise is not for them, so they quit it. But more often, "giving up" is a process, and a slow one at that. More often, we gradually find ourselves caring less and less about a thing. Then one day we realize we simply gave up.
Many failed marriages fit this example. Many couples who decide to divorce state that they gradually realized they were "out of love." It wasn't sudden, it was gradual.
Many spiritual problems also fit this example. Many people begin praying expectantly, loving God and looking for him to answer their prayers. But when their answers are slow to come, or are not what they expected, the luster prayer begins to dim, until one day, they realize they haven't prayed in over a week. Nor do they miss it.
This may be why Jesus teaches a parable in Luke 18:1-8 about a persistent widow. Luke tells us that Jesus told his disciples this parable "to show them that they should always pray and not give up" (18:1, TNIV). Some translations state it slightly differently. For example, the NRSV says, "Then Jesus told them a parable about their need to pray always and not to lose heart."
To give up is to lose heart, to lose your passion for something. Why would Jesus be concerned about such a thing among his disciples? Jesus knows that, surrounded by injustice, it is easy to focus on problems, rather than trusting God to deliver. The way to continue trusting God is in prayer. But when prayer does not seem to be answered, doubts will sometimes arise.
In this context, Jesus tells a parable about a persistent widow and an unjust judge. A widow had to continually appear before a judge to plead her case and ask for justice. But for whatever reasons, the judge refused her case. Finally, because of her relentlessness and persistence, he saw that she received justice.
But, Jesus says, your God is not like this judge. Our God is just, not unjust. Our God is not slow to deliver, he is quick. There is no doubt about God's plan and intentions.
What Jesus is more concerned with is our faith. He wonders, "when [he] comes, will he find faith on the earth" (18:8)? Our challenge is not to lose heart. Our challenge is to recognize that God's actions and timing are just and quick. We may not see it that way, but it is not for us to question God. Rather, we are to be people of faith, a faith that will be noticeable when Jesus comes looking for it.
So what will faith look like? Such a faith will persevere and will not give up. Though life is challenging and difficult, the faith Jesus is looking for is a faith that lasts. It endures. The foundation of such faith is prayer--prayer that recollects God and his work among us; prayer that never gives up; prayer that continually prays for the justice of God to be seen in our world.
Such prayer works, and causes the one praying to work. When Jesus wonders whether he will find faith, he challenges us to keep on keeping on. When the going gets rough, will we give up, or stay with it? Because we know that God will bring his justice, we need to keep praying for, and working towards, the day of his revealing.