27 As Jesus went on from there, two blind men followed Him, crying out, “Have mercy on us, Son of David!” 28 After Jesus had entered the house, the blind men came to Him. “Do you believe that I am able to do this?” He asked. “Yes, Lord,” they answered. 29 Then He touched their eyes and said, “According to your faith will it be done to you.” -Matthew 9:27-29 BSB
A Christian’s faith is not the source of healing. Jesus is the source. Jesus only responds when we exercise our faith in believing that He can do what we ask of Him if it’s according to His will (1 John 5:14).
In James 1:5-7, it says that if you ask God for wisdom but you doubt that He will give it to you, then do not expect to receive it. God will only act on your prayer when you believe that He can and will do it, giving you spiritual wisdom and knowledge.
6 And without faith it is impossible to please God, because anyone who approaches Him must believe that He exists and that He rewards those who earnestly seek Him. -Hebrews 11:6 BSB
A faithless person cannot expect to please God or even think that they will have their prayer answered. To some extent, this applies to a genuine believer in Jesus Christ. If we go to Jesus with doubt when we pray, don’t expect an answer from the Lord. But, if we are honest with the Lord and say to Him, as we see in Mark 9:24, which says, “Immediately the boy’s father cried out, “I do believe; help my unbelief!” That type of honesty Jesus answers because He knows our weaknesses and inadequacies. The boy’s father came to Jesus, saying to Him that he was struggling with faith. He had faith mixed with doubt. Even though the Scriptures didn’t say what happened to his weak faith after Jesus helped his son, we can logically conclude that his doubts went away when Jesus healed his son.
Seeking the Lord through prayer and reading God’s Word is how one’s faith gets stronger and doubt is pushed out.