Even when we do act on our faith, symptoms do not always disappear instantly.
After Hezekiah was healed, it was three days before he was strong enough to go up to the house of the Lord. (See 2 Kings 20:1-5).
In John 4, the nobleman "believed the word that Jesus had spoken unto him" (v. 50), and when he met his servants, he inquired of them the hour when his dying son "began to amend" (v.52).
The Bible differentiates between the "gifts of healing" and the gift of "the working of miracles" (1 Cor. 12:9).
Christ could do no miracle in Nazareth because of the people's unbelief, but He healed a few sick ones (Mark 6:1-6). If everyone were to be made perfectly whole instantly, there would be no place for the gifts of healing; it would be all miracles.
Many people miss healing by trying to confine God to miracles. Christ's promise is that "they shall recover" (Mark 16:18), but He does not say "instantly."
"Faith means that we are confident of what we hope for, convinced of what we do not see" (Heb 11:1, Moffatt). We are "convinced," of course, because God, who cannot lie, has spoken. How all-sufficient is this reason for believing! Faith is, therefore, most rational.
It is not, as many unthinking persons suppose, believing without evidence, but believing because of the very highest possible evidence, God's Word, which is "settled in heaven" (Ps. 119:89).
The apostle James said, "I will show you by my deeds what faith is!" (James 2:18, Moffatt). Faith, therefore, is being so convinced of the absolute truth of the declarations of God that are recorded in the Bible that we act on them.