This is not to say that God doesn't want you well or will not heal you, just that each case is different and God alone knows what to do about each one. The primary message behind this article is that when you are sick or in need of anything.......TRUST HIM.........

No one gets to have perfect health for a lifetime; at some point everyone deals with health issues. This is just a fact of our imperfect earthly lives and mortal bodies. We are flawed, imperfect human beings who need God for everything. And God does everything in accordance with His Will, which we mere mortals have no way of comprehending, but God wants that we trust Him, whether we understand or not. God doesn't expect us to understand why He chooses to not heal someone, just that we trust Him to have a reason and a purpose in everything He does and everything He allows. 

God may heal us and while there's nothing wrong in asking and believing for it, but it helps to know that if it doesn't come, that is not an indication of a lacking faith. In fact, God may have a plan for something good in your life or someone else's life, through your condition. Patience is paramount. But most important is that, even if complete healing doesn't come, He'll still take care of us in our infirmities. 

God always has a purpose for everything He does. Sometimes He heals for His Glory. Sometimes He chooses to not heal someone in order to call that soul unto Himself. God uses our weakness and suffering to work through, to show Himself through or to teach us something. The Bible teaches that God uses suffering to make us better; to refine and polish us through testing, so we may learn and grow:

1 Peter 1:6-9

"In this you greatly rejoice, though now for a little while, if need be, you have been grieved by various trials, that the genuineness of your faith, being much more precious than gold that perishes, though it is tested by fire, may be found to praise, honor, and glory at the revelation of Jesus Christ, whom having not seen you love. Though now you do not see Him, yet believing, you rejoice with joy inexpressible and full of glory, receiving the end of your faith—the salvation of your souls."

1 Peter 4:19

"Therefore let those who suffer according to the will of God commit their souls to Him in doing good, as to a faithful Creator."

1 Peter 5:10

"But may the God of all grace, who called us to His eternal glory by Christ Jesus, after you have suffered a while, perfect, establish, strengthen, and settle you."

Romans 5:3-5

"And not only that, but we also glory in tribulations, knowing that tribulation produces perseverance; and perseverance, character; and character, hope. Now hope does not disappoint, because the love of God has been poured out in our hearts by the Holy Spirit who was given to us."

Moreover, our suffering keeps us needing and relying on Him.

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1Peter 4:12--

"Beloved, do not think it strange concerning the fiery trial which is to try you, as though some strange thing happened to you;"

Although Jesus was moved to compassion and healed many; He did it for His Glory as a demonstration of God's existence, through His Loving Power.
Sometimes God uses suffering in order to bring about something good, as we learn in Genesis 20:50:

"But as for you, you meant evil against me; but God meant it for good, in order to bring it about as it is this day, to save many people alive."

"And we know that all things work together for good to those who love God, to those who are the called according to His purpose." (Romans 8:28)

Other times, sickness may be a test. Sometimes it's in order to grow our trust for Him. Whatever the reason, the main thing is to TRUST HIM, even when we do not understand.

Our world is wrought with disease and all kinds of suffering, which all began at the fall of man that happened in the very beginning, in the Garden of Eden, but when Jesus returns to set up His Kingdom on earth, He will eradicate all sickness and pain, as we read in Revelation 21:4.

As the Apostle Paul taught in 2Corinthians 12:7 and Peter explains in 1Peter 5:10, God is all we need and because we believe and rely on Him, we can rest in His Sovereignty. And in 2Corinthians 12:7, Paul says this:

"And He said to me, “My grace is sufficient for you, for My strength is made perfect in weakness.” Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me. Therefore I take pleasure in infirmities, in reproaches, in needs, in persecutions, in distresses, for Christ’s sake. For when I am weak, then I am strong." (2Corinthians 12:9-10)

God used Paul's suffering to draw him closer. See Romans 3:23-25 & Ephesians 1:7, and Acts 9.

Moreover, believers have no real cause to fear death, inasmuch as we know Christ overcame death and the grave, therefore, all true believers will spend eternity with Him.

"O Death, where is your sting? O Hades, where is your victory?” (1Corinthians 15:55-57)

"that whoever believes in Him should not perish but have eternal life. For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. For God did not send His Son into the world to condemn the world, but that the world through Him might be saved." (John 3:15-17)

Our spiritual condition is more valuable than our physical condition.

"Behold, I have refined you, but not as silver; I have tested you in the furnace of affliction." (Isaiah 48:10)

Note: The Book of Job is also a good one to read on this subject.