As to faithfulness, it is to those who have believed. And are already saved. And the purpose or goal of faithfulness is not salvation, but reward.
Here it what Peter says,
in direct opposition to your words.
20 For if, after they have escaped the pollution's of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning.
21 For it would have been better for them not to have known the way of righteousness, than having known
it, to turn from the holy commandment delivered to them. 22 But it has happened to them according to the true proverb: “A dog returns to his own vomit,” and, “a sow, having washed, to her wallowing in the mire.”
2 Peter 2:20-22`
One only has to read these words to know that people that have faith, are faithful.
They are faithful to not turn from the holy commandment, that was delivered to them.
Not holy commandments, [plural], but the holy commandment.
The holy commandment of the Gospel is Repent... for the kingdom of God is at hand.
Repent means to turn to God, and by default turn away from Satan as lord, to Jesus as Lord.
The term Repent is about changing kingdoms by changing the Lord you serve.
This is what Paul was sent to do by Jesus Christ.
17 I will deliver you from the
Jewish people, as well as
from the Gentiles, to whom I now send you, 18
to open their eyes, in order to turn them from darkness to light, and from the power of Satan to God, that they may receive forgiveness of sins and an inheritance among those who are sanctified by faith in Me.’
Acts 26:17-18
The way we are forgiven of our sins, as a lost person, is by obeying the Gospel command to repent, not repent of our sins, but repent, which means to turn to God. The Gospel is about changing which Lord we serve, from Satan to Jesus.
When we repent,
we are forgiven our sins.
This concept is clear in Peter's words.... look at what he says, the
linch-pin statement by which a person who has escaped from the power of Satan, escaped from the pollutions of this world, through the knowledge of the Lord Jesus Christ,
and has become ensnared and overcome again,
leading to a far worse condition than when they were unbelievers.
For it would have been better for them not to have known the way of righteousness,
than having known it, to turn from the holy commandment delivered to them.
Repent is turn to God, and by default turn way from Satan as lord.
To "turn from" the holy commandment is to
"un-repent" or to turn back from Jesus as Lord, and being overcome again as a slave to the domain of darkness.
When we repent and turn to Jesus as Lord and confess Him, we are transferred out of the dominion of darkness into the kingdom of God.
13 He has delivered us
from the power of darkness and
conveyed us into the kingdom of the Son of His love, 14 in whom we have redemption through His blood, the forgiveness of sins.
Colossians 1:13-14
So, according to Peter, it is only those who are faithful, and faithful to the end that will receive the salvation of their souls.
6 In this you greatly rejoice, though now for a little while, if need be, you have been grieved by various trials, 7 that the genuineness of your faith,
being much more precious than gold that perishes,
though it is tested by fire, may be found to praise, honor, and glory at the revelation of Jesus Christ, 8 whom having not seen you love. Though now you do not see
Him, yet believing, you rejoice with joy inexpressible and full of glory,
9 receiving the end of your faith—the salvation of your souls. 1 Peter 1;6-9
...receiving the end of your faith, the salvation of your soul.
JLB