In the New Testament, miracles were signs given to unbelievers to bring them to Christ. Just as tongues (foreign languages) were given to spread the Gospel, so the miracle of healing testified to God’s power. 1 Corinthians 14:22 (NKJV), “Therefore tongues are for a sign, not to those who believe but to unbelievers;…”
The great Apostle Paul could heal others, but he could not heal himself. In fact he prayed for healing three times, and God said no. Paul wrote about this in 2 Corinthians 12:7-10 (NIV), “…Therefore, in order to keep me from becoming conceited, I was given a thorn in my flesh (probably poor eyesight)…Three times I pleaded with the Lord to take it away from me. But he said to me, ‘My grace is sufficient for you, for my power is made perfect in weakness.’ Therefore I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me. That is why, for Christ's sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong.”
When we are sick, whether it is from actual diseases or emotional stressors, we tend to draw closer to God. We turn to Him for strength and comfort. These experiences develop our characters and our relationships with God. Christians need to recognize that God uses both blessings and trials to help us to rely on Him and on His powerful love.
Respecting unbelieving mankind, God has promised to restore humanity to the perfection lost in the Garden of Eden. Acts 3:21, (NIV), “Heaven must receive him until the time comes for God to restore everything, as he promised long ago through his holy prophets.” This will happen when Christ establishes His reign on Earth at His return.
In the resurrection, all mankind will have the opportunity to be healed from diseases and restored to perfect health. Isaiah 35:5-6, 9-10 (NIV), "Then will the eyes of the blind be opened and the ears of the deaf unstopped. Then will the lame leap like a deer, and the mute tongue shout for joy. Water will gush forth in the wilderness and streams in the desert . . . No lion will be there, nor any ravenous beast; they will not be found there. But only the redeemed (Jesus redeemed all – “in Christ shall all be made alive.”) will walk there, and those the LORD has rescued will return. They will enter Zion with singing; everlasting joy will crown their heads. Gladness and joy will overtake them, and sorrow and sighing will flee away.”
Revelation 22:2, “…on either side of the river, was the tree of life, which bore twelve fruits, each tree yielding its fruit every month. The leaves of the tree were for the healing of the nations.”