It's all about taking God at His Word, and trusting in His promises.
When the world comes crumbling down, God's children will continue to stand. We are bombarded daily with fiery darts from the devil, daily we must die to ourselves to keep this walk God has chosen for us. Sometimes the battle gets hard and we begin to doubt. Fear creeps in and the devil whispers, "You'll never be healed." But faith boldly proclaims, "But God said I am already healed! These symptoms are only lying vanities."
If the devil was a human, he'd be a sweet faced liar.
Being able to stand on God's Word and proclaim your healing takes faith. If you don't have a lot of faith, saying it will help build it. When the devil sweeps in and whispers doubt, say, "But God said victory is mine! But God said the devil already lost! But God said I am His child!" Not only will saying this help build your faith, it blacken the devil's eyes, and that's always a fun little bonus.
Honestly, it's like one of those commercials that keep going on and on about a non-stick pan... "But wait, there's more!"
This little phrase But God Said can be used in nearly every aspect of your Christian walk. Feeling alone? But God said He would never leave you. Feeling beat down? But God said He would restore your strength. Feeling lost? But God said I am the truth, the life, and the way. Feeling guilty for sins in your past? But God said your sins are forgiven! Honestly, someone should write a song about this. But God said! You can't argue with it. The devil shoves something at you, shove those three words at him and then make a joyful noise.