Jesus was given authority over all the power of the enemy to undo the works of Satan.
Luke 10:19 - Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you.When we are authorized to come against the enemy and subdue him there is nothing to stand in faith's way.
Without the believer's authority there is great danger as told at a later time.
Acts 19 (King James Version) - 13Then certain of the vagabond Jews, exorcists, took upon them to call over them which had evil spirits the name of the LORD Jesus, saying, We adjure you by Jesus whom Paul preacheth.
14And there were seven sons of one Sceva, a Jew, and chief of the priests, which did so.
15And the evil spirit answered and said, Jesus I know, and Paul I know; but who are ye?
16And the man in whom the evil spirit was leaped on them, and overcame them, and prevailed against them, so that they fled out of that house naked and wounded.
17And this was known to all the Jews and Greeks also dwelling at Ephesus; and fear fell on them all, and the name of the Lord Jesus was magnified. Authorized ones are known by our enemy.
Because of what Jesus has done we can have healing as part of the salvation package of God. Deliverance is also part of it and the authority of Christ by His shed blood at calvary is given to us to use to undo the works of the devil who has had the authority from God to harm anyone disobedient to God and His word.
Faith teaches us to repent and receive the salvation package, a gift from the great God Jehovah Who has all authority to authorize what He will. Jesus said 'I come to do the will of Him Who sent Me.' Faith recognizes authority and moves to do the impossible.