Why do some people get healed immediately after prayer, but others never get healed, even after praying for a long time?
The short answer is, we don’t know why God chooses to heal some, but not others—at least not for each individual case. Therefore, I’m hesitant to ever answer the question beyond this.
While there are many possible answers, the most helpful answer I have found is that the kingdom of God has not fully come yet. On the one hand, the kingdom of God is coming and near.
Matthew 10:7-8~ “As you go, preach this message: ‘The kingdom of heaven is near.’ Heal the sick…”
But on the other hand, the kingdom is still something future (Matt 7:21) and, therefore, we continue to await the redemption of our bodies.
Romans 8:23~ “We ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for our adoption as sons, the redemption of our bodies.”
We must remember that all of our bodies fail. Even those who are healed now eventually have their bodies fail when they die. But, all believers will eventually be healed at the resurrection with the “redemption of our bodies” (Rom 8:23).
This doesn’t explain why one specific person is healed now instead of another person, but it does temper the expectation that some people have that everyone should be healed today.
Please notice that I have not said anything about faith. God does respond to faith (Matt 9:22), but the amount of faith a person has does not have anything to do with whether or not the person is healed, as least not for Christians. No level of faith assures healing. And one can always pray, “I believe; help my unbelief!” (Mark 9:24).
God in Suffering
Christians are sometimes too prone to look for God only in the victory of Christ’s resurrection, and by analogy in the victory of our present healings. However, we need to remember that God was also present in the suffering of the cross of Christ, and by analogy in our present sufferings.
In the midst of suffering, we can affirm with Paul that God’s “grace is sufficient” (2 Cor 12:9). Hence, just as we pray (and should pray!) for God to heal people, we can also pray for God’s grace to endure suffering, even though to some that mistakenly seems like a capitulation to our suffering.