It is a false teaching, that God has somehow promised His people divine healing in this life from every illness.
This false teaching causes a disruption in trust in the truthfulness of the Bible, since obviously God does not miraculously heal most of His loved ones today.
Even worse, some of these false teachers claim falsely that Christ died on the cross to purchase our miraculous physical healing in this life.
Thus, the false teaching of the promise of divine healing is propped up with a viciously false doctrine of Calvary.
There is no doubt that God does heal. He "forgives all our iniquities, and heals all our diseases." Anytime we are healed of a sickness, it's the Lord's ultimate doing, though it is usually not miraculous in nature.
God heals most often through the physical mechanisms He placed in His creatures. Our skin closes up over time when we are cut; our immune system kicks in to overwhelm infections; bones knit by the mechanism God gave our physical bodies.
All of these are healing from God! They are astounding, and we ought never take them for granted!
Sometimes, God directly interposes by miracle to divinely heal His people.
No doubt Jesus miraculously healed a host of people, and raised some of them from the dead, and sometimes He gave to His disciples the power to heal miraculously. After Pentecost, His apostles and others carried out notable healings on their command, by the power of the Holy Ghost.
We should pray for divine healing! No doubt God does miraculously heal some people today!
But miraculous healing is not promised by God to all who seek it at this time.