You are right. The inner thoughts are as important as what we do. I too have known people that have fallen. Some were even ministers of the Word. The Bible says: "Let anyone that thinks he stands take heed lest he fall." When I say I would never do something I am not saying it is impossible I am expressing my intention never to go that way.
Pride is a dangerous thing for a believer to harbor. We need Him and it is when we know the flesh is weak that we depend on Him the most. When Peter bragged that he would never deny Christ he thought he could meet the challenge in his own strength but it was a spiritual battle that he could have only prepared for by prayer.
The principle of strength out of weakness comes from Paul but it is basic to the principle of the cross. I am not speaking here about the historic work of the cross for our salvation. I am speaking about the work of the cross that should be going on inside us daily. This is a truth Paul came to understand before the others. At least he wrote about it. The redemption, the new covenant, the forgiveness of sin was in prophecy but the exchanged life was an extension of the truth of the cross based on our identification with His death.
12 So then, brethren, WE are under obligation, not to the flesh, to live according to the flesh-- 13 for IF you are living according to the flesh, you will die; but if by the Spirit you are putting to death the deeds of the body, you will live. 14 For all who are being led by the Spirit of God, these are sons of God (Romans 8:12-14)
These verses will, hopefully, convey what I am trying to communicate.
First he says brethren so we know he is talking to Christians
Next he says we are under obligation. Some people think there are no obligations or imperatives in our walk but there are and this is one of them. An obligation is a responsibility we can either take up or ignore.
IF we are living according to the flesh we will die. The "if" is a conditional. If it was not possible for Christians to live according to the flesh Paul would not have needed to say this to them.
In order to live above the flesh Paul says we have to be led by the Spirit (walk in Him). Through His power we are enabled to transcend the flesh and be like Christ. But I believe we are conformed to the image of Christ progressively (2 Corinthians 3:18).
Only Christ's life in us can produce the image of Christ. This work is blocked when we put confidence in our own ability to be like him (Philippians 3:3). I do not see how anyone could argue that God does not want us to obey. Of course he does but even that we must do through Him.
I learnt the same teachings.
LA