I agree with you. But this statement is about the realm of spiritual warfare. When doubt comes to us in order to discourage us, we are to stand on the word of God and declare what He says. God will commission us to do things we feel we can't do, but He says we can. When we feel inferior to the task, we are to declare that God is with us and therefore we can do all things through Him. When we declare the word of God we destroy the lies of doubt that come to detour us from expanding His kingdom and setting the captives free.
I too believe we are to also clean the inside of the cup. In worship to Him, and confessing of our sins, asking His forgiveness, we allow God to come in and purify our hearts. Never burry what God want to get rid off. I think this is one of the hardest parts of being in a relationship with God. Often times we want to hide the pain we carry, or the past sins we have committed. It's hard to open up, even to God because we have to allow ourselves to be vulnerable to Him. Once we get past that, He is so faithful and gentle to us that He cleans our hearts with the utmost care. He is such a great and loving Father!
Thank you so much for your comment. I do completely agree with you and all you have said.