Jesus healed many people during his time of ministry and many of those physical healing were because of their spiritual illnesses. Most of the times when there is a physical illness it is difficult to tell its origin, and that is why we go to doctors. Doctors study medicine and learn to detect illnesses. The bible teaches us that in these end times there is going to be an increase in science or knowledge (Dn12:4). The fact is that God found it important that we have doctors to help us rely on one another to certain extent, but there are some things that, like some healing, he wants to and can do himself. And, sometimes those illnesses linger within us without being properly diagnosed, because they are deeply routed, and no medicine can take them away just like the women with the issue of blood. That, for twelve years she bled and could not find a cure, she went to every doctor with no avail (Mt9:22). It was not until she tapped into her faith and that in Jesus that this women with the issue of blood got healed. The bible teaches us that by his stripes we are made whole (Is53:5).
Mark 2: 9 Which is easier: to say to this paralyzed man, ‘Your sins are forgiven,’ or to say, ‘Get up, take your mat and walk’? 10 But I want you to know that the Son of Man has authority on earth to forgive sins.”So he said to the man, 11 “I tell you, get up, take your mat and go home.” 12 He got up, took his mat and walked out in full view of them all. This amazed everyone and they praised God, saying, “We have never seen anything like this!”
Now, these friends faithfully were carrying their friend to Jesus, we do not know how long was this man sick or paralyzed, but we know that the persistent faith of these guys played a factor for him to be healed. Such persistent faith suggests that this guys will was fired up by his friends faith and not of his own. We are our brother's keepers, and through our persistent faith we can help cause a healing on our friend or love ones; we must not give up. The sickness this man had was related to something he did bad, and maybe he had forgotten; because most of things that we do that are not right we cast them to the back burner of our brain, just like Cain did with Able (Ge4:9). Jesus came with all the authority from heaven (Lk4:36, Jh5:26-27). So, some illnesses requires spiritual authority (v10) such as is from heaven to come out, and this person needed forgiveness of sins in order to be healed. Like many of us who cannot shake certain illnesses of which we are probably due because of an infraction in the past and need forgiveness.