Well then, I suppose where we stand after all of this is that my salvation is assured and yours isn’t unless you continue to satisfy your obligations.
Not quite. You *think* your salvation is assured (based, I'd argue, on a misunderstanding), and I think my salvation is not yet assured.
I didn't invent this. When Jesus said (twice, in the same Gospel [Matthew]) that "he who endures to the end will be saved", it's not reasonable to assume that He said such a thing (and repeated it, for emphasis) pointlessly. When Jesus warns us about something (especially if more than once), it must be a true threat. There are numerous other Scriptures to that effect, and NO Scriptures which guarantee salvation unconditionally (regardless of whether we keep sinning grievously or not).
Look... I completely understand that the idea of "once saved, always saved" is tempting and attractive, at least at first glance; the idea of "breathing a sigh of relief" and being "on" to do good works simply because it'd be a "nice thing to do" appeals to us, especially since we humans (including Christians) are so prone to fall into sin (and somesimes grave sin). It'd be a bit like an employer guaranteeing my salary for life, and guaranteeing me that--no matter what I did--I could never be fired, but that "if I'd continue to teach my classes, it'd be very good of me, and befitting a good employee, and an appropriate way to show my gratitude for the immense free gift".
But haven't you noticed that we humans (even those who have accepted Christ) can sometimes be pitifully UN-grateful? We have to ask the question: what of those who've "accepted Christ" (whatever that means to any given faith group), and have then "backslidden"? (That term, by the way, is not usually a Catholic one; it came into frequent use in Evangelical/Revivalist circles, mainly.) What if a "backsliding" Christian simply chooses NOT to reform his life, at least partially because he sees no need (and that various sins and sinful tendencies--especially sexual ones--are intoxicating and titillating and enjoyable, and he doesn't want to give them up)?
I've heard a variety of non-Catholic Christian answers to this:
1) "That person was never truly Christian in the first place!" Well... HE certainly THOUGHT he was! If a retroactive declaration of "he was never a Christian in the first place" can be used, then it could be used on YOU, should you fall into habitual sin in the future... and as such, your "guarantee of salvation" was no more real than HIS was. (I.e. you won't know if you're a "real" Christian until you die, and until it's too late to change... which is hardly what "once-saved-always-saved" offers as an assurance.)
2) "They're still saved, but a sinful lifestyle robs them of the JOY of their salvation!" This has two problems: first, it's a gross injustice to those who're being HARMED by this person's sins in the meantime; and second, this really seems to disregard Who God Is, and why He made us in the first place (i.e. to unite Himself to us as intimately as a bridegroom with a bride, and to unite us to each other--hence the two great commandments: "Love God, and love neighbor"). Anyone whose character has become laden with vice (i.e. evil habits) will not WANT to be in Heaven! Heaven will be more intolerable to them than Hell! At any rate: it's hardly a fitting justice for a life of sin to say that "you really didn't enjoy yourself as much as you could have, had you lived a life of virtue!"
3) "The sinful life will make the sinner suffer in THIS lifetime, and he'll be paid back plenty!" While there's a great deal of truth to the idea that sin will empty one's life of joy and will tend to visit evil on the sinner, that's nowhere near a universal guarantee; it's proverbial that "the evil flourish and the good suffer", and this life doesn't come close to redressing that. (Ironically, Protestantism [with all due respect] really doesn't know what to do with human suffering, whereas the Catholic Church's rich teaching on redemptive suffering makes sense of it in a way that nothing else does--it's one of the most consoling things about Church teaching, in fact, and the rest of the world just tries to ignore or self-medicate or euthanize the pain away.) It may seem like semantics, but it's really quite critical: the idea of "I've accepted Jesus once, so now I'm all set" is akin to a husband saying "I love you" on his wedding day, and then never saying it again (the so-called "joke" goes that he says to his complaining wife, "I told you I loved you 30 years ago; if that ever changes, I'll let you know!"). That relationship will wither, and it might die.
That's the horrid thing about Luther's error, in this regard: it reduces our RELATIONSHIP with God (which means nothing, if it's not ongoing and bi-directional) to a mere JURIDICAL arrangement; it replaces a marriage with a judicial acquittal. UNLIVING things can sometimes be kept intact without maintenance; but LIVING things need care, lest they sicken and die. That's true of our hearts and souls, as well; our relationship with God can sicken and die, if we neglect it, just as a houseplant can sicken and die if we forget to water it and prune it and get it adequate sun. No one is saying that we "made" the water and pruning shears and sunlight; but if we don't USE them, our souls can die.
Re: the idea of "worrying about salvation" vs. "assurance": at the risk of making this long, I want to post something from a Saint who was well-acquainted with suffering, sin, and the blessed virtue of divine Hope--St. Claude de la Columbiere (not well-known, but he's a spiritual master):
"An Act of Hope and Confidence in God
by Saint Claude De La Colombiere
My God, I believe most firmly that Thou watchest over all who hope in Thee, and that we can want for nothing when we rely upon Thee in all things; therefore I am resolved for the future to have no anxieties, and to cast all my cares upon Thee.
People may deprive me of worldly goods and of honors; sickness may take from me my strength and the means of serving Thee; I may even lose Thy grace by sin; but my trust shall never leave me. I will preserve it to the last moment of my life, and the powers of hell shall seek in vain to wrestle it from me.
Let others seek happiness in their wealth, in their talents; let them trust to the purity of their lives, the severity of their mortifications, to the number of their good works, the fervor of their prayers; as for me, O my God, in my very confidence lies all my hope. "For Thou, O Lord, singularly has settled me in hope." This confidence can never be in vain. "No one has hoped in the Lord and has been confounded."
I am assured, therefore, of my eternal happiness, for I firmly hope for it, and all my hope is in Thee. "In Thee, O Lord, I have hoped; let me never be confounded."
I know, alas! I know but too well that I am frail and changable; I know the power of temptation against the strongest virtue. I have seen stars fall from heaven, and pillars of firmament totter; but these things alarm me not. While I hope in Thee I am sheltered from all misfortune, and I am sure that my trust shall endure, for I rely upon Thee to sustain this unfailing hope.
Finally, I know that my confidence cannot exceed Thy bounty, and that I shall never receive less than I have hoped for from Thee. Therefore I hope that Thou wilt sustain me against my evil inclinations; that Thou wilt protect me against the most furious assults of the evil one, and that Thou wilt cause my weakness to triumph over my most powerful enemies. I hope that Thou wilt never cease to love me, and that I shall love Thee unceasingly. "In Thee, O Lord, have I hoped; let me never be confounded."
Now, St. Claude was as Catholic as I am (and a far better one)... but does this sound like someone who's despairing or fretting over every last little thing, regarding his salvation? The Catholic Church offers not just a comparable "assurance" which you seem to be wanting, but She offers one based in truth and the fullness of the Faith.