You still do not understand justification by grace through faith. So let's take a mundane example. A criminal also has a brother who is an upstanding citizen. The criminal murders an innocent person, is convicted, and sentenced to death. The upstanding brother loves his no-good brother so much that he offers to take the death penalty in his place. The judge agrees since justice will be served. The criminal goes Scot-free while his brother dies in his place.
That is what justification means. Your sins do not affect your justification since Christ paid the penalty for your sins. Does that mean that you can return to your evil ways? Absolutely not. You needed to repent in order to be justified by grace. Therefore you now need to live soberly, godly, and righteously. And you will do so if you know what it cost the Savior and you truly believed on Him.
Of course I understand it.
Psalm 85:5
I will hear what God the LORD will say; For He will speak peace to His people, to His godly ones;
And may they not turn back to foolishness.
What "foolishness"?
Psalm 69:5
God, You know my foolishness, And my guilt is not hidden from You.
As the Law says
Deuteronomy 4:6
So keep and do
them, for that is your wisdom and your understanding in the sight of the peoples who will hear all these statutes and say, ‘Surely this great nation is a wise and understanding people.’
The DOING of the Law was "wisdom"--and the inference is that if you BREAK the Law it is "folly".
So what is the "folly" they are not to return to?
Sin.
Let them not return to
sin.
Same thing 1 Corinthians 10 is teaching.
Why is there "no condemnation for those in Christ"? Because they're no longer slaves of sin by which they had been automatically bringing condemnation on themselves with their sin... but if you go back to sin, you will bring condemnation on yourself just as Romans 14:23 teaches.