If you understand how God views sickness, then you will never again doubt its source. God calls sickness “captivity”: And the LORD turned the captivity of Job … (Job 42:10).
Jesus came to preach deliverance to the captives:
The Spirit of the Lord is upon me, because He hath anointed me to preach the gospel to the poor; He hath sent me to heal the brokenhearted, to preach deliverance to the captives, and recovering of sight to the blind, to set at liberty them that are bruised … Luke 4:18
Jesus called sickness bondage:
And ought not this woman, being a daughter of Abraham, whom Satan hath bound, lo these eighteen years, be loosed from this bond on the sabbath day? Luke 13:16
Jesus came to set people free with the truth:
And ye shall know the truth and the truth shall make you free (John 8:32).
The truth is that Jesus viewed sickness as oppression and healed those who were oppressed:
How God anointed Jesus of Nazareth with the Holy Ghost and with power: who went about doing good, and healing all that were oppressed of the devil; for God was with Him. Acts 10:38
The Bible identifies death as an enemy:
The last enemy that shall be destroyed is death (I Corinthians 15:26).
Sickness is called loathsome:
For my loins are filled with a loathsome disease: and there is no soundness in my flesh (Psalms 38:7).
It is also viewed as evil:
An evil disease, say they, cleaveth fast unto him … (Psalms 41:8).