Had a short lesson on erroneous faith teachings, and here are a few good points: (will keep it short)
1. Even if it seems like a good thing, if it isn't in the will of God, it shouldn't be done.
Do you realise that out of all the sick people by the pool of Bethesda, Jesus only healed one man? That He didn't heal the lame man at the gate of the temple? Jesus went according to what the Father moved Him to do. When God remained silent, Jesus didn't presume that the time was perfect for the work.
In 2 Kings 20, when God told the godly king Hezekiah, who was sick and dying, that his time on Earth was almost up, he didn't want to die so he prayed to God in tears that he would live longer. God did hear his prayer and decided to grant him fifteen more years, but they were bad years, years of mistakes that only made him a more sinful man.
Always remember that we act in faith in response to God's own INITIATIVE. Something that seems logically good might not be in the will of God. Not everything in the Bible given to individuals is also specifically for you and me.
Exodus 33:15 If Your presence does not go with us, do not bring us up from here.
(Also, a point to note: Good, godly men who are honoured by God can also get sick to the point of death. God heals, but He's also sovereign over what happens to our lives. Timothy was sick (1 Tim 5:23). Paul was sick (Gal 4:13). Even Elisha died of sickness (2 Kings 13:14). I once heard a pastor (of a certain church that I really respected and loved) talk about how this guy had fallen ill with cancer, and how if he had been a Christian, he might not have gotten it. I was like WOAH. Christians do fall sick too, and more often than not, it has nothing to do with lack of faith or deviance from God.)
2. Just because God can do it for you, it doesn't mean He will.
He is still sovereign. He has the ability to make 'all grace' abound towards us, but maybe He has something better in store for the development of our character. So? Does it mean we stop trusting in Him? Do we have faith in the healing, or in the God who heals?
The last one is something I've always believed, and I'm so glad he brought it up:
3. If anyone is fully, entirely certain about his theology, he's probably wrong.
One simple reason. How can a limited, finite man fully comprehend an unlimited, infinite God?
With a lot of things regarding theology, people are extremely aggressive or defensive regarding what they believe. Every theology or concept - all human ways of understanding God - is made up of a zillion major and minor parts. Maybe we're all partly right. Maybe we're all totally wrong. Just because a few minor points are errant (to someone else), it doesn't make the entire concept invalid.
I believe in both evolution and intelligent design. If each were a circle in a Venn diagram, I believe they are more overlapped than separate. I'm not going to bother explaining it now, but in Genesis, God created the sea creatures, then birds, then land animals, then man - why can't he have formed them all from a single process? Are we limiting His ability? Are we trying to comprehend His own reasoning, and then dismissing the idea when we can't seem to read His mind?
I'm probably wrong. It's okay. I'm open to people's viewpoints, and each person's opinion opens up a whole range of new possibilities. We don't know. It's okay. We have to come to a point where we acknowledge, and are comfortable with, the fact that we don't know it all.