Since both Catholics and Protestants can see that concupiscence remains in the baptized, how each group defines it determines whether God blots out sin in our souls or merely covers sin with the righteousness of Christ.
For Protestants, since concupiscence is sin and it remains after baptism, this sin “obviously” is merely covered by God’s grace.
For Catholics, since concupiscence is not sin (since no free will is involved) our souls are pure after baptism, not merely covered over.
What verses in Scripture support the Catholic view that sin must be a free will choice in order for it to be sin?
I didn’t think that concupiscence was in the evangelical vocabulary because the theology I often encounter is that the we cannot be sinless while on earth.
Concupiscence is the inclination to sin it is not in and of itself sin.
It
does remain after baptism though the stain of the sin of Adam does not. Though the penalty for a sin may be cleansed and forgiven the temporal punishment for it remains.
An example would be if you physically damaged your hand for punching someone who forgives you for your violent act because you repented. Though you are forgiven of your act your hand is still damaged. Sin is death to the flesh and forgiveness does not make the flesh immortal.
CCC:
405 Although it is proper to each individual, original sin does not have the character of a personal fault in any of Adam’s descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ’s grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.
1264 Yet certain temporal consequences of sin remain in the baptized, such as suffering, illness, death, and such frailties inherent in life as weaknesses of character, and so on, as well as an inclination to sin that Tradition calls concupiscence, or metaphorically, “the tinder for sin” (fomes peccati); since concupiscence “is left for us to wrestle with, it cannot harm those who do not consent but manfully resist it by the grace of Jesus Christ.” Indeed, “an athlete is not crowned unless he competes according to the rules.” 2 Tim 2:5.
Because we are sinners doesn’t mean we have to commit sin.
We can sin accidentally by weakness or intentionally by choice.
Both are sin though obviously the choice to sin would be make one more culpable of the sin.
Ignorance of the law is not and excuse even though the Lords Mercy prevails over our weakness.
We are called by the Lord to resist the temptations to sin.
It takes an act of the will and the help of Gods grace to succeed in resisting and mortifying our concupiscence.
CCC:
2515 Etymologically, “concupiscence” can refer to any intense form of human desire. Christian theology has given it a particular meaning: the movement of the sensitive appetite contrary to the operation of the human reason. The apostle St. Paul identifies it with the rebellion of the “flesh” against the “spirit.” (Gal 5:16,17,24; Eph 2:3. )
Concupiscence stems from the disobedience of the first sin. It unsettles man’s moral faculties and, without being in itself an offense, inclines man to commit sins.
978 "When we made our first profession of faith while receiving the holy Baptism that cleansed us, the forgiveness we received then was so full and complete that there remained in us absolutely nothing left to efface, neither original sin nor offenses committed by our own will, nor was there left any penalty to suffer in order to expiate them. . . . Yet the grace of Baptism delivers no one from all the weakness of nature. On the contrary, we must still combat the movements of concupiscence that never cease leading us into evil "
You can find here:
“Reconciliation and A Biblical Portrait of Sin”
that may contain the scriptures your seek or you might try searching the footnotes of the CCC.