'... the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death'. Chapter 8 verse 2.
From that time onwards this was his testimony, 'there is therefore now no condemnation to them that are in Christ Jesus (who walk not after the flesh but after the Spirit) for the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death'. It is intensely personal. He was not setting down teaching, he was recounting his experience; 'this is what I have found', he is saying, and O how precious it was to him. We are told that the words in parenthesis above are not in the most ancient and more reliable manuscripts, from which we may infer that they were not in the original epistle. They are an exact copy of Paul's words in verse four, and so the scribes, whoever they were that copied out the sacred text, are not to be thought guilty of inserting thoughts of their own, even if it was their idea to put the phrase higher up in the text. May we not infer that by doing so those people have revealed to us that they too had discovered the reason for Paul's rejoicing? He found he could walk after the Spirit and not after the flesh, and so had they.
How wonderful this experience is, and how glorious it is to every man who similarly discovers that the law of the Spirit of life in Christ Jesus has made him free from the law of sin and death. What light in darkness, especially when it is coupled, as it is here, with the fact that there is therefore no condemnation to him because he really and recognizably is in Christ Jesus. Whenever Paul's doctrine touches upon human experience of salvation it is always based on his own experience, and what glorious doctrine it is; because of this it is the gospel indeed, God's good news and man's good news in one. If the note of personal testimony is missing from gospel preaching it is a vain hope, for what at first is an enlightening message and liberating hope will die away into darkness and condemnation. That is why Paul spoke about walking not after the flesh but after the Spirit; unless a man can do that, he has no testimony that his beliefs are right, no proof that his doctrine is correct; he is just believing in unworkable theories. The walk in the Spirit is the sole proof that the law of the Spirit of life in Christ Jesus has indeed set a person free from the law of sin and death. For if there is one thing that is absolutely certain, it is that dead men cannot walk; legs and feet they may have, but life they have not.
(From the book - The Doctrine of the Holy Spirit in Romans)