Yes that scripture out of context gives the impression that Paul the apostle status is like you describe: But if you read the chapter before and the chapter after that verse you realise that Paul is desrcibing the status of imself when he was a religious man and did not have the spirit of Christ in him. To me "abiding in Christ" means to be living in Christ's character.
You are wrong on my taking this out of context. If Paul is discussing how he was before Salvation, why then does he use the present tense in saying I am carnal, sold under sin. Paul calls himself the chief of sinners. 1Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I
am chief. This letter was written to Timothy toward the end of Paul's life and he uses present tense.
Php 3:4 ¶ Though I might also have confidence in the flesh. If any other man thinketh that he hath whereof he might trust in the flesh, I more:
5 Circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, an Hebrew of the Hebrews; as touching the law, a Pharisee;
6 Concerning zeal, persecuting the church; touching the righteousness which is in the law, blameless.
7 But what things were gain to me, those I counted loss for Christ.
8 Yea doubtless, and I count all things but loss for the excellency of the knowledge of Christ Jesus my Lord: for whom I have suffered the loss of all things, and do count them but dung, that I may win Christ,
9 ¶ And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:
10 That I may know him, and the power of his resurrection, and the fellowship of his sufferings, being made conformable unto his death;
11 If by any means I might attain unto the resurrection of the dead.
12 Not as though I had already attained, either were already perfect: but I follow after, if that I may apprehend that for which also I am apprehended of Christ Jesus.
13 Brethren, I count not myself to have apprehended: but this one thing I do, forgetting those things which are behind, and reaching forth unto those things which are before,
14 I press toward the mark for the prize of the high calling of God in Christ Jesus.
Paul says he has not yet attained perfection.
read Hebrews 10:26-31, and then you can tell me if we are able to willfully sin.
This passage is saying that if we go on sinning deliberately without any change after we are saved, there is no longer a sacrifice of sins. Paul goes straight from saying we have full assurance of faith, and that we need to stir up each other to love and good works (v.24), to saying if we go on sinning deliberately there is no longer a sacrifice of sins. i.e I get "saved", but I deliberately continue to commit adultery against my wife. This would mean that I was most likely never truly saved. That is what Paul is hinting at here.
If I say that now I will be a lier, because I have not yet quite finished to crucifing my flesh with its passions and desires, all I can say is that by the grace of God I am well on the way to do just that, Why? because I know what God requires of me.
It is written in John 1:12 that Jesus has given us a right to become children of God, for it says. But as many as received Him, to them He gave the right to become children of God, even to those who believe in His name. Thus once the Lord has approved us, we should be able to identify ourselves with the words of 1 John 3:2-12 for in them we find what we should be looking forward to, and who we really are destined to be, as we read: Beloved, now we are children of God, and it has not appeared as yet what we shall be. We know that, when He appears, we shall be like Him, because we shall see resemble Him just as He is. And everyone who has this hope fixed on Him purifies himself, just as He is pure. Everyone who practises sin also practises lawlessness; and sin is lawlessness. And you know that He appeared in order to take away sins; and in Him there is no sin. No one who abides in Him sins; no one who sins has seen Him or knows Him. Little children, let no one deceive you; the one who practises righteousness is righteous, just as He is righteous; the one who practises sin is of the devil, flesh for the devil flesh has sinned from the beginning. The Son of God appeared for this purpose that He might destroy the works of the devilflesh. No one who is born of God practises sin, because His seed abides in Him; and he cannot sin, because he is born of God. By this the children of God and the children of the devil flesh are obvious; anyone who does not practise righteousness is not of God, nor the one who does not love his brother. For this is the message which you have heard from the beginning, that we should love one another; not as Cain, who was of the evil one, and slew his brother. And for what reason did he slay him? Because his deeds were evil, and his brothers were righteous.
You cannot substitute the word flesh for devil. The devil is not flesh. The devil is spirit. Also, this refers to Christ's appearing in His full glory, which He has not yet done, other than to three of His disciples. When Christ returns in His glory, we will then be transformed to be like Him. Sin is who we (humans) are not what we do. Sin is our nature.