Hebrews 11:6 And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.
Whilst we may still doubt our faith at times, Jesus does not doubt us or limit His love and mercy toward us.
When He talked about how much faith we needed, it was not a description of a huge bucket full but the smallest of seeds the Jews knew of instead.
Jesus knows we do doubt things, but He also knows that a tiny spec of faith shows Him we love Him and that pleases Him; for that Christ is willing to reward us!