Faith for healing is not a result of striving and struggling to believe. It is not a mental force but rather a spiritual force. Faith comes from hearing the word of God (Romans 10:17). The reason for this is that the word of God reveals the will of God. If I can know what God's will is concerning any area, I can approach Him with perfect faith to receive what He desires to give me.

"Now this is the confidence that we have in Him , that if we ask anything according to His will, He hears us. And if we know that He hears us, whatever we ask, we know that we have the petitions that we have asked of Him." 1 John 4:14-15

For You are the Lord Who heals me. Exodus 15:26

So I shall serve the Lord my God, and You will bless my bread and my water. And You will take sickness away from the midst of me and You will fulfill the number of my days. Exodus 23:25-26

Bless the Lord, O my soul; and all that is within me bless His holy name!
Bless the Lord, O my soul, and forget not all His benefits:
Who forgives all my iniquities, Who heals all my diseases,
Who redeems my life from destruction, Who crowns me with lovingkindness and tender mercies,
Who satisfies my mouth with good things, so that my youth is renewed like the eagle's. Psalm 103:1-5

You sent Your Word and healed me, and delivered me from my destructions. Psalm 107:20

Father, I give attention to Your words; I incline my ears to Your sayings. I do not let them depart from my eyes; I keep them in the midst of my heart; for they are life to me, and health to all my flesh. I keep my heart with all diligence, for out of it spring the issues of life. Proverbs 4:20-23

Father, You desire that I prosper in all things and be in health, just as my soul prospers. 3 John 2

Since the Spirit of Him Who raised Jesus from the dead dwells in me, He who raised Christ from the dead is giving life to my mortal body through His Spirit Who dwells in me. Romans 8:11

(Jesus) Surely You have borne my sicknesses and carried my pains; Yet You were esteemed stricken, smitten by God and afflicted. But You were wounded for my transgressions, You were bruised for my iniquities; the chastisement for my peace was upon You, and by Your stripes I am healed. Isaiah 53:4-5

Who Himself bore my sins in His own body on the tree, that I, having died to sins, might live for righteousness - by Whose stripes I was healed. 1 Peter 2:24