Also, you did not grow up in that culture to know if they did not speak that way.
Nor did you. That's how these arguments work. It doesn't really mean anything because no one alive today is a native Koine Greek speaker.
However, scholars have . . . oh nevermind, you know about all of that . . .
So if you believe Paul’s words, then how do you believe his words in Galatians 5:24 and 2 Corinthians 7:1?
How do believe Peter’s words in 1 Peter 4:1-2?
1 Peter 4:1-2 KJV
1) Forasmuch then as Christ hath suffered for us in the flesh, arm yourselves likewise with the same mind: for he that hath suffered in the flesh hath ceased from sin;
2) That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God.
Just like Jesus, be resolved to suffer, it's cleansing.
1 Peter 4:3 KJV
3) For the time past of our life may suffice us to have wrought the will of the Gentiles, when we walked in lasciviousness, lusts, excess of wine, revellings, banquetings, and abominable idolatries:
Let it be enough, the lusts of the flesh, if you suffer, God is purifying you.
To answer directly to your question, how does this passage speak towards whether if a Christian sins he stops being a Christian, the presupposition to this passage is that there is sin to be ceased from, and so suffering comes to accomplish that. (Of course, this is taking in a broader context than just the two verses.)
Rather than casting His children because of continued sin, God speaks of helping us through suffering to cease from that sin. This is affirmed also in Hebrews 12, that God will in fact train His children, and that His training will in fact be effective.
Galatians 5:22-25
22) But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
23) Meekness, temperance: against such there is no law.
24) And they that are Christ's have crucified the flesh with the affections and lusts.
25)
If we live in the Spirit, let us also walk in the Spirit.
I'm not sure your thought here, but this saying is affirmed in a number of places.
Towards your question about whether sin causes you to stop being born again, IF we live in the Spirit, this is the condition to be met, and if you meet it, the subsequent admonition is for you, Let us also walk in the Spirit. The presupposition here is that you may be alive in the Spirit but not also walking in the Spirit, and to you it is said, "Let us also walk in the Spirit". If being alive in the Spirit is one and the same with walking in the Spirit, this verse would be a tautology. There is a reader whom Paul addresses who is alive in the Spirit though not walking in the Spirit.
Which happens to harmonize with Paul's writing in Romans 7 showing his current state of living.
2 Corinthians 7:1 KJV
1) Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.
This is much the same thing.
Are you thinking I'm arguing against holy living? Because I'm not.
Much love!