Romans 7: 19 For the good that I would I do not: but the evil which I would not, that I do. 20 Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me.
Without true conversion which the indwelling Christ brings, not only Peter, but every other human being for that matter, would use their freedom of choice to foster and indulge evil tendencies and propensity that are lodged in our DNA, and therefore it is not a matter of merely changing behaviors; a new heart and mind must be installed into our persons by God Himself.
There are very well-behaved persons out there, in the secular world, who are Atheists, and who, as far as track record goes will beat many Christians hands down. Yet, vestiges of our fallen human nature will be manifest at some level and in different ways and situations, in those persons, sometimes without any warning whenever the right set of circumstances do converge.
The Bible states this truth unequivocally, so that no one be deceived as to the gravity, and depth of the sin problem in us. Yes, we can and must choose, but the problem goes much deeper than merely choice.
Romans 7:21 I find then a law, that, when I would do good, evil is present with me. 22 For I delight in the law of God after the inward man: 23 But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members.
May God add His blessing to the study of His word. “Good night” and God bless!