Yes Tenchi it is our faith that justifies us, and Jesus Christ gives that faith, by giving HIs faithfulness for us to believe in, ( His Gospel) and the Spirit for us to follow Him. ( believe He died to give us His flesh and HIs blood, which is living, so we live rise with Him.)Then our justification is not of Christ, but of our faith, isn't it? If we maintain our justification by faith, then it is our faith, not our Saviour, by which we are justified. This seems to me to be what is implied by your statement here.
We trust in Christ as our justification. In him, we are justified, his perfect righteousness is imputed to us, and we are, thereby, made acceptable to God. But having been justified, we are fundamentally changed, and adopted into God's family, and cannot go back to what we were before, no matter how we live. A caterpillar that has become a butterfly, has been changed such that, even if it were to behave like the caterpillar it used to be, it would still be a butterfly. Some things - like God making us alive spiritually and adopting us as His own - cannot be reversed or undone.
Well, the believers at Corinth show that this isn't the case. They had been spiritually circumcised and yet were carnal, sinful people. Their sin didn't dissolve their adoption into God's family, however (though, it did greatly hinder their fellowship with Him). So, spiritual circumcision can't be undone by disobedience, but not because the "circumcised" can't disobey, but because they can't undo God's work upon them.
Well, then there are verses like the following that clarify and qualify the ones here that you've offered:
1 John 1:8-10
8 If we say we have no sin, we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
10 If we say we have not sinned, we make him a liar, and his word is not in us.
From the ESV:
1 John 3:9-10
9 No one born of God makes a practice of sinning, for God’s seed abides in him, and he cannot keep on sinning because he has been born of God.
10 By this it is evident who are the children of God, and who are the children of the devil: whoever does not practice righteousness is not of God, nor is the one who does not love his brother.
1 John 5:18
18 We know that everyone who has been born of God does not keep on sinning, but he who was born of God protects him, and the evil one does not touch him.
From the NASB:
1 John 3:9-10 (NASB)
9 No one who is born of God practices sin, because His seed abides in him; and he cannot sin, because he is born of God.
10 By this the children of God and the children of the devil are obvious: anyone who does not practice righteousness is not of God, nor the one who does not love his brother.
As has been pointed out many times, John was speaking to a habit, or persistent practice, of sinning, to a life of sin, not to a believer who is struggling with sin, trying to overcome it, and sometimes falling into it. Many want to make John say something about sin in the verses above that directly contradicts many other parts of Scripture - like Paul's letter to the Corinthians or Galatians.
All of that ( belief) is what saperates circumision ( of Christ) from non circumcision ( in the flesh)
Also as pointed out to you many times, if they commit sin, they are the uncircumcision. ( Jew and Gentile.)