Your question is not in line with what the Scriptures teach.
Why not? Please answer my question - Does
practicing righteousness and not sin (1 John 3:9-10) include forgiving others their trespasses? Or are those who are born of God characterized as unforgiving?
Again, this would be a pointless teaching even to an unbeliever. Because if they become a believer then they are going to automatically forgive according to your beliefs.
So you have two different camps of believers? Believers who forgive and are forgiven and believers who refuse to forgive and are not forgiven? Do those two camps also include believers who "do not practice sin but practice righteousness" and believers who "practice sin and do not practice righteousness?" Where does John mention those two "separate" camps of those who are born of God in 1 John 3?
It is also silly to suggest that Jesus is talking to unbelievers because they have no spiritual understanding unless they repent of their sins and believe.
So what you are really trying to imply is that if a believer gets angry with someone over a trespass and has a temporary weak moment of un-forgiveness, that believer is back to being lost in his sins all over again until he forgives that person? Saved, refuse to forgive, lost salvation, repent, confess saved again and the wheels on the bus go round and round? Do you believe that the majority of genuine born again Christians will end up in hell due to their continued lack of forgiving others, but of course, this does not include you?
Like I said before, it does no unbeliever any good to forgive others if they do not repent of their sins and accept Christ.
How many unbelievers would genuinely forgive someone from their heart over an unthinkable terrible trespass against them (rape, murder of family member etc..) apart from the love of God in their heart/Holy Spirit? How many genuine believers forgive others from their heart solely in their own strength? Matthew 6:12 says And forgive us our debts,
As we forgive our debtors.
If an unbeliever forgives and that is all they do, then they will still not be forgiven because they have not accepted Christ yet. So we know Jesus here is speaking to believers and not unbelievers.
Regardless, continued unforgiveness is the mark of an unbeliever and forgiveness would be the mark of a genuine believer. We should forgive others because God, through Christ, has forgiven us. *Ephesians 4:32 - And be kind to one another, tenderhearted, forgiving one another, just as God in Christ forgave you. I don't see any warnings from Paul here that temporary weak moments of failing to do so will lead to cancelled salvation. That would be performance based works salvation. Is it law or grace? It is inconceivable that someone who has truly experienced God's forgiveness, is a new creation in Christ and has received the love of God in their heart by the Holy Spirit who was given to them would continually stubbornly refuse to forgive others their trespasses. Just doesn't fit.
For the mysteries of the Kingdom are not even given to unbelievers. It would just go in one ear and out the other.
It's not only unbelievers who listen to things that go in one ear and out the other.