Contrary to common belief, the Bible does not teach that all men are the children of God. Our Lord said to the religious leaders of His day: “Ye are of your father the devil” (John 8:44), but to the Christian believers at Galatia St. Paul wrote: “Ye are all the children of God by faith in Christ Jesus” (Gal. 3:26).
As the children of Adam, it is not strange that we should have to bear suffering; for sorrow, sickness and death entered the world through sin (Rom. 5:12). But some people wonder why God’s children, whose greatest desire is to please Him, should have to suffer along with others.
There are several reasons for this. In the case of Job, God allowed His servant to suffer to prove to Satan that Job did not live a godly life for personal gain — and Job was richly rewarded later for all he had borne.
Further, God’s people could not be of much spiritual help to others if they were exempt from the sufferings which others have to bear. In such a case the unsaved would say: “Yes, you can talk! You don’t know what it is to suffer disappointments, sickness and pain, as we do.”
Then too, it must be remembered that even the most godly saint is not perfect and must at times be disciplined, “for whom the Lord loveth He chasteneth, and scourgeth every son whom He receiveth” (Heb. 12:6). This is done for our good, to keep us from sin and its consequences.
Finally, suffering and adversity tend to make God’s children pray more and lean harder on Him, and herein lies their spiritual strength and blessing. St. Paul said: “I take pleasure in infirmities… for when I am weak, then am I strong” (II Cor. 12:10).
But there is a great twofold advantage which the suffering Christian has over others. First, his sufferings are only temporary and, second, they earn eternal glory for him.
“For our light affliction, which is but for a moment, worketh for us a far more exceeding and eternal weight of glory” (II Cor. 4:17). source