You seem to have an unbiblical view of justification. Justification (imputed righteousness) is a one-time act of God, and it is never reversed. To be justified means to be declared righteous, and the basis of justification is (1) God's grace and (2) the finished work of Christ for our redemption. But only those who obey the Gospel are justified. That includes (1) repentance toward God and (2) faith toward our Lord Jesus Christ.
But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness. (Rom 4:5)
Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all (Rom 4:16)
And therefore it was imputed to him [Abraham] for righteousness. Now it was not written for his sake alone, that it was imputed to him; But for us also, to whom it shall be imputed, if we believe on him that raised up Jesus our Lord from the dead; Who was delivered for our offences, and was raised again for our justification. (Rom 4:22-25)
This does not mean that Christians must not address their present sins or fail to examine themselves. In fact those who have received the grace of God must live soberly, righteously, and godly in this present world (Titus 2:11,12)
Sorry, but our argument fails on account of being illogical, not to mention being unscriptural. You say justification is “a one-time act of God and is never reversed … only those who obey the Gospel are justified”, but then you argue that after being once-and-forever justified, a Christian “
must live soberly, righteously and godly in this present world.” No, there is no “must” - if justification is once-and-forever, the justified-forever Christian
does not have to “live soberly, righteously and godly in this present world”.
According to your theology, after having been once-and-forever justified, a Christian can then live a life filled with all sorts of evil and sin and still be “justified” - because according to you, justification “is never reversed”.
So having been justified by “obeying the Gospel”, the justified-Christian can then
disobey the Gospel and still be justified. In fact, according to you, the once-and-forever justified Christian can even lose his faith and still be justified. That is absurd.
According to you, if a serial killer, for example, comes to Christ and repents of his sins, he is justified forever ... but then having been (supposedly) justified forever, he can lose his faith, return to being serial killer … and still be justified forever. Your theology doesn’t add up.
Obviously, justification is NOT once-and-forever - it is CONDITIONAL - a Christian is justified ONLY IF HE OBEYS THE GOSPEL. If he disobeys the gospel, he can lose his justification.
So what you should have said is, “those who have received the grace of God must live soberly, righteously and godly in this present world to REMAIN JUSTIFIED.” Paul makes this clear when he warns believers in Gal 5 and 1Cor 6 that their sins can result in them not inheriting the kingdom of God - he also warns believers in Romans 6 that their sins can “lead to death”.
To be justified means to be declared righteous
Being “declared righteous” does not mean being declared eternally justified and eternally saved. You can go from being “declared righteous” to being “declared
un-righteous”. Abraham was “declared righteous”, but later God tested his faith by commanding him to sacrifice his son Isaac. So obviously, being “declared righteous” in not the end of the story - it is only the beginning of the story. Being justified in not the end of the story - it is only the beginning of the story. Having been initially justified, you must REMAIN justified by faith and righteous living (aka, faith and works).