Matthew 5:48
Be perfect, therefore, as your heavenly Father is perfect

James 1:6&7

But when he asks, he must believe and not doubt, because he who doubts is like a                                    wave of the sea, blown and tossed by the wind.  That man should not think he will receive anything from the Lord.
Galatians 3:6
Consider Abraham:  "He believed God, and it was credited to him as righteousness."