We see one of the mistakes of King Asa below.
“And, behold, the acts of Asa, first and last, lo, they are written in the book of the kings of Judah and Israel. And Asa in the thirty and ninth year of his reign was diseased in his feet, until his disease was exceeding great: yet in his disease he sought not to the LORD, but to the physicians.” - 2 Chronicles 16:11-12, also see 1 Kings 15:23.
In 2 Kings 1:1-18 we can read of one of the mistakes of King Ahaziah.
King Ahaziah was sick and he sent messengers to “enquire of Baalzebub the god of Ekron” as to weather or not he would recover. Then the angle of the LORD said unto Elijah “Arise, go up to meet the messengers of the king of Samaria, and say unto them, Is it not because there is not a God in Israel, that ye go to enquire of Baalzebub the god of Ekron? Now therefore thus saith the LORD, Thou shalt not come down from that bed on which thou art gone up, but shalt surely die. And Elijah departed.” Elijah met the messengers and told them the words of the angle of the LORD. The messengers returned to the King and told him what Elijah had spoken. In verse 17 we see that King Ahaziah died according to the word of the Lord which Elijah had spoken.
We can see the certain death Ahaziah faced for seeking after false gods instead of the LORD. Some “Christian” people do this same thing because they do not believe direct healing from God is possible. I in no way advocate disregarding doctors. I simply mean that God can work healings apart from them.
In the age of modern medicine in which we live there are at least three points to be remembered. First, all credit for healing must ultimately be given to God. Second, our faith must ultimately be placed in God for healing, not in man. Third, we must remember that what man says is impossible, is possible with God, as he wills for his glory. I see no reason for God to heal those who would not give him the praise and glory for it, though he sometimes does simply because he is so kind and gracious (John 11:4, Luke 17:12-19). And I believe that if we had greater faith, we would see more miracles (Matthew 13:58). It also must be remembered that the physical diseases that distress us may be for our spiritual benefit (Romans 8:28, Matthew 18:8, 2 Corinthians 12:7, 2 Corinthians 12:9-10). The gift of healing is one of the gifts given by the Holy Spirit (1 Corinthians 12:9, 1 Corinthians 12:30). And contrary to the lies taught by some, all of the gifts listed by the Apostle Paul still exist in the Church today as God grants them. There is no Biblical reason to think otherwise.
“O LORD my God, I cried unto thee, and thou hast healed me.” -Psalm 30:2
“Who forgiveth all thine iniquities; who healeth all thy diseases” -Psalm 103:3
“Why art thou cast down, O my soul? and why art thou disquieted within me? hope thou in God: for I shall yet praise him, who is the health of my countenance, and my God.” - Psalm 42:11 (also see the nearly identical Psalm 43:5)
Also see 2 Corinthians 4:16, Proverbs 17:22, Deuteronomy 32:39, Psalm 147:3, and James 5:14-16.
“Hast thou not known? hast thou not heard, that the everlasting God, the LORD, the Creator of the ends of the earth, fainteth not, neither is weary? there is no searching of his understanding. He giveth power to the faint; and to them that have no might he increaseth strength. Even the youths shall faint and be weary, and the young men shall utterly fall: But they that wait upon the LORD shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.” - Isaiah 40:28-31