The issue is not(for christians) IF God can work through any man. Yes He can. The issue is for christians what Gods will and desire for us is.
Does God desire more that His children should be treated with doctors and scientists and methods of the world, that often cause reactions, side effects, money etc... and that give Him little glory and take no or little faith?
OR
Does God desire more that His children look to His promises and work on the cross and covenants trusting only in Him so that all glory is given to Him and Him alone, to recieve His grace which is free, perfect, with no side effects, no reactions, no lasting damage, where faith in Him is walked in, as the just shall live by faith and where they rely on Him as their faithful Dad in all matters of their lives which really are not even their own but belong to him?
Now the arguement is being made that God can work through sciencists, men beleivers or unbeleievers. TRUE. The question is what is the biblical example of what God desires and provides and does for HIS children? What do we see more in scripture, Gods people coming to HIM for healing, deliverance, repentance, forgiveness, provision by faith and recieving it or them going to the world?
Why did Jesus not walk around directing people to go see the physicans or try some medicines first? Why did he tell all who came to him by faith that they were healed, their faith has made them whole? Why does God give healing promises all through the word of God and even call himself YHWH RAPHA The Lord my HEALER.
If God desires more that His people should seek unbelievers or medicines or doctors why does He makes covenatal promises about healing us? Why did Jesus take stripes to heal us and to bare our sicknesses on His body?
Isa 53:4 ¶ Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.
Isa 53:5 But he [was] wounded for our transgressions, [he was] bruised for our iniquities: the chastisement of our peace [was] upon him; and with his stripes we are healed.
Now many say that His stripes only spiritually heal us, but the same verse is shown in scripture to be for physical healing as well as also deliverance from demons.
Mat 8:16 ¶ When the even was come, they brought unto him many that were possessed with devils: and he cast out the spirits with [his] word, and healed all that were sick:
Mat 8:17 That it might be fulfilled which was spoken by Esaias the prophet, saying, Himself took our infirmities, and bare [our] sicknesses.
People often do not connect the dots all together. Jesus bore our curse becomming a curse for us by hanging on a tree. All death and sickness and bondage came from the fall of sin upon man and Jesus died to redeem us and set us free of the totality of the curse.
Christians should live and walk by faith. that is the only way to please God and that is how the just live. Now faith is a walk and some have more faith than others and some have heard the word of God more than others by which our faith grows and increases.
If a person is sick and they do not yet have the faith then they should use wisdom and go to a doctor because their faith will not carry them through a trial of faith in that matter yet, but that does not mean they should do so without also using that as an opportunity to believe God for healing in smaller matters and to hear the word of God in that area that their faith may grow, that they will walk justly and pleasing coming to know God better and trust him more fully so that as they grow more and more glory in their lives will be given to God alone without physical means for what is already spiritually accomplished.