Who says sickness is to our benefit? There are Christians who think this, that we ought to be grateful for our afflictions and find in them lessons God is teaching us .
In the writings of the Rev JR Miller which overall I like, yet I do not agree with him that sicknesses are blessings.
My major argument is that Jesus Christ spent a huge amount of time healing every kind of sickness. He wanted us to have life abundantly. How can anyone who is in pain have that?
First of all this is a very difficult and personal topic which doesn't have a clear answer.
As others have mentioned, yes, this is a way for God to call you but what doesn't make a lot of sense to me is when children get sick.
That is very difficult for me to understand.
Because as an adult you'd have to internalize, rationalize and process a LOT of things when you get sick before you get to some sort of peace inside. Because nobody understands suffering until you get suffering. Then when you get it, your first reaction is anger, denial and disbelief. Peace is the last word in the vocabulary.
But when you do get peace it means that you had growth.
However a child can't do any of that, so i'm not sure why a child would have to get sick.
In regards to Jesus healing the sick, that was a way for Him to show that He had control of nature and the laws of nature by doing these miracles.
But, these miracles continue to this day after prayer and being in sacred holy places. It doesn't always work, which is another mystery, but when it does it defies all the experts and rational thought and it's considered A Miracle.
So some people are healed and others are not.
Bottom line is that it's a difficult subject and hopefully you arrive at peace which is also what Paul had when he said that he was content with everything and whether he lives or dies, it's for The Lord.