Everything but your I John cite is pre-Calvary.
Different deal in-play at that time.
God had not executed Jesus in anybody’s stead, yet; they were each accountable before Him for their own sin.
NOT-SO-SIDEBAR:
David’s psalm is a FABULOUS primer on true repentance, and — boy howdy — if there’s one thing the whole world needs a ton more of, it’s repentance, but even David’s wholesale repentance isn’t a salvific belief in the shed blood of Jesus, because that hadn’t happened, yet. That heart — that heart after God’s heart — that insatiable thirst to be in The Presence, and in fellowship; that should be our model for how to repent well.
The Matthew 18 cite is really interesting because it reveals something about forgiveness. The wicked servant was forgiven the debt; and his punishment was erased. But when he, himself would not forgive, as he had been forgiven, his unforgiveness evidenced that his prior repentance was not genuine — just crocodile tears to get out of his debt. Fake repentance didn’t save him from his debt, and — on top of that — his unforgiveness toward his fellow servant left him subject to torment.
God has forgiven us PERFECTLY. When we believe that this is so, that awareness of His immense kindness toward us evokes a true repentance that is our “YES” to that forgiveness. As we grapple with sin in this world, we may come back to the foot of the cross and refresh our embrace of that forgiveness again and again, but Christ was still only crucified once for ALL of our sins — past, present and future. Sin you commit today was known — and forgiven — way back at The Cross; it HAD to be, otherwise Jesus would never be able to come down off of that Tree; he’d be stuck there bleeding continually for the ongoing sins of humanity, “for without the shedding of blood, there is no remission from sin.”
So, “If we confess our sins...” isn’t speaking of a present-day confession minting new forgiveness from God; it’s our intentional, repentant opt-in to the forgiveness He already wrought in executing His Son in our stead; us saying, “Yes, Father, I reaffirm my wholesale acceptance of Your terms. THANK YOU for executing Jesus instead of me! And ‘Thank YOU,’ Jesus, for being willing to take my place.”
The only detail left to address is what ends up happening to those who won’t confess.
“And the rest [those who would not repent, confess, and believe] were killed with the sword which came from the mouth of Him who sat on the horse...”
The ultimately unrepentant are EXECUTED by God The Son PERSONALLY, in a PERFECT enactment of Romans 6:23 — “The wages of sin is Death.”
The deal expires, and you don’t get the benefit.
"Forgive us."