Who said that one becomes ever deserves Salvation? It is a pure gift from God. Even after sin, Salvation can be had merely by repenting and asking for it, but one does need to repent. So I will ask again: can someone remain in serious sin and still be saved by faith alone? Paul says no, what say you?
Paul says ‘examine yourselves whether you be in the faith. THAT should tell you that those who remain in sin are not in the faith to begin with. It is GOD Who is in you both to do and to will of HIS good pleasure. You are boguth with a rpice. You didn’t pay the price, Jesus did. It is He Who owns your soul and spirit ... and He said ‘raise up a child in the way that theu should go and they will not depart from it’. Is there a better parent than The Lord God Creator? How much credit do you demand from God for your eternal life? Or is it your eternal state of death that you are earning. You will exist eternally, in one state or the other.
Of course not. The two things are mutually exclusive, because "faith comes through hearing the Word of God." Once that has happened, one becomes surrendered to the Holy Spirit, and sin starts to fall away. In the case of a child or someone who is a terrible sinner but calls out to God as he is dying in a car crash, he will be judged like the thief who died on the cross beside Jesus; the sincerity of his belief and shame at the life he has led would be considered, the same way Jesus told that man, "Today you will be with me in paradise."
I believe that there are a lot of elements of Roman Catholicism (which probably would have been my family's cultural heritage but for a strange twist of fate) that were welded into it due to its location in the dense village/town life of Europe, and the Roman Church's function as the government under the Holy Roman Empire. The pre-literacy millenium fostered a close regulation and examination by the priest caste and the town elders of other people's sins. The focus on the Great Commission and the joys of salvation and the gospel became intertwined, pre-Gutenberg, with managing the inherent scandals of village life.
This is not to say that the Reformation is without its own downside: it's just that no human institution is or can be infallible. Reformation concepts took natural root in the freedoms of America and its vast undeveloped frontiers. This led to a powerful form of individual responsibility not just in society, but for one's relation to the Christ, but also to the excesses and heresies endemic to "too much" freedom. But for those free to study the Word from many translations and seek the Truth directly through the guidance of the Holy Spirit and prayer, the journey from craven sinner to repentant sinner is deep and genuine.
In either tradition, Catholicism or Prot/Evang/Reform, I'd estimate fewer than 10% really study the Word, the tenets of their denomination and understand what they are doing, what it means to participate in the Eucharist, and be in daily communication with the Lord. The rest understand parts and many are just there from habit, family tradition or (gasp) virtue signalling.