Where is the explicit teaching in Holy Scriptures that souls who have been regenerated lose their justification and imputed righteousness from God through and in Christ?
Let me first ask you a simple question. Do not the scriptures EXPLICITLY warn you that should you take the mark of the beast, you will suffer eternal torment? Would you still have Jesus' 'imputed' righteousness then? If you evade answering this question, possess a crystal ball and are 100% certain that you would never take the mark and thus deny Christ, just remember that Peter who walked and talked with Jesus daily was absolutely certain that he would not deny Christ; yet we all know what happened to Peter. And why would you not take it? After all, don't you believe that you can never lose you justification??
That is why we are admonished to continue in the faith -
if indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard, which has been proclaimed in all creation under heaven, and of which I, Paul, became a minister. Col 1:23
The word "if" indicates only the possibility - not the certainty - that one will in fact continue in the faith. "If indicates a condition - stable, steadfast, not shifting - that must be met by us in order to continue in the faith.
The Apostle Paul warned the brethren in Rome that
if they live according to the flesh (habitual sin), they will die (Rom 8:13). The Apostle James wrote:
"My brothers, if anyone among you wanders from the truth and someone brings him back, let him know that whoever brings back a sinner from his wandering will save his soul from death and will cover a multitude of sins. " Js 5:19-20
The Apostle John wrote "Little
children,
let no one deceive you. Whoever practices righteousness is righteous, as he is righteous.
Whoever makes a
practice of sinning is of the devil, for the devil.... 1 Jn 3:7-8
The numerous warnings in Scripture against apostatizing from the faith are written to believers; not unbelievers. It is impossible for an unbeliever to depart from the faith since he/she was never a part of the faith to begin with. The notion that true believers can never die spiritually and lose their justification/salvation is a lie. It is just another lie from Satan - the same lie that the serpent spoke to Eve in Gen 3:4
"You will not certainly die," the serpent said to the woman."
Don't believe the lie.