This is an important topic for Christians, as it's crucial to our Salvation. To continue in sin knowingly certainly results in a loss of one's Salvation. We must forsake that sin(s) and do our first works over by being cleansed in the blood of Jesus for the remission of sin. If we cling to that sin(s), we are fallen from grace and are considered backsliders.
Romans 6
[1] What shall we say then? Shall we continue in sin, that grace may abound?
[2] God forbid. How shall we, that are dead to sin, live any longer therein?
[3] Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?
[4] Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
[12] Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof.
[13] Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.
[14] For sin shall not have dominion over you: for ye are not under the law, but under grace. (KJV)
What's odd in your use of
Romans 6 is that Paul was writing to
Christians, to born-again people, to whom he was having to explain the nature of their spiritual identity and condition in Christ and the need to yield themselves unto God. Obviously, if they had been living in these things already, he would not have had to remark on them to the believers at Rome. But, apparently, they weren't, and so to them he asked with rhetorical incredulity, "How shall we, who are dead to sin, live any longer therein?" In
Romans 6, though, Paul never indicated that these ignorant and sinning believers had lost their salvation.
This is the same sort of thing observable in Paul's letter to the believers at Corinth (
1 Corinthians 3, 5, 6, 11). He pointed out a number of sinful things in their attitudes and conduct, things they were willfully persisting in, and one thing that was even grossly sexually immoral (
chapter 5), and yet he constantly affirmed that, despite their willfully sinful behavior, they were
still God's own. For example, Paul identified the Corinthian believers as "
carnal babes
in Christ," (
1 Corinthians 3:1), and accused them of fractious, partisan, ego-driven sin (
1 Corinthians 3:3-4), but in the same chapter called them God's "field" and "house" (
vs. 9), "brethren," (
vs. 1), and wrote, "you belong to Christ" (
vs. 23) and that they were the "temple of God" (
vs. 16). It seems very plain to me that Paul did not think willful sin meant a believer had lost their salvation. The same thing is true of Paul's letter to the Galatians, as well.