When it comes to having confidence as a Christian, our confidence is not based upon a theory or unsubstantiated promises but on the very character and nature of our loving Father God.
You can have confidence that God is who God says He is; therefore, you are who God says you are.
God can do what God says He can do; therefore, you can do what God says you can do.
And because God has what God says He has; therefore, you have what God says you have.