1 John 1:9 "If we confess our sins..." is a very misused verse, but it is really very simple at its face value, even by itself, if you look at it closely in the original text and pick it apart.
The first part is εαν ομολογωμεν τας αμαρτιας ημων,
transliterated "ean [h]omologomen tas [h]armartias [h]emon" (Latin/Roman character font)
εαν, transliterated "ean," is a contraction of "ei" ("if") and "an" (meaning a "supposition")
ομολογωμεν, transliterated "[h]omo-log-omen," is a combination of "homo," which means "same" or "like," just like it is used as an English word prefix, plus a verb form of "logos" which means "word" or "saying," with the verb ending "omen," which means means "we may/should." The verb form is present tense, subjunctive mood. So it is "we-may/should-be-same-wording"
τας, transliterated "tas" = "the"
αμαρτιας, transliterated "[h]a-martias" = "sins," is any "failure" or "fault" (see LSJ entry "ἁμαρτία").
ημων, transliterated "[h]emon" = "of us" (genitive case)
Putting all that together, εαν ομολογωμεν τας αμαρτιας ημων, transliterated "ean [h]omologomen tas [h]armatia [h]emon," hyper-literally means "if-suppose we-may/should-be-same-wording the failures of-us"
The root words "homo-logos" are important here. We need to avow, acknowledge, make a "like-statement" about our sins. "Like" who, or "like" what, you ask? Well, like, that should be obvious. Like what the truth is about them, and what God says about our sins! We've committed sins, there is no changing the historical fact of it, they are unacceptable, and Jesus paid the price to remit (i.e. pardon, forgive) them.
Also, as you've probably heard preached many times, "sin" = "[h]armartia" = any failure, anything that "falls short of the glory of God" (Rom 3:23), which is why the Greek word for "failure/fault" is used, and not the Greek word for "evil/malice/depravity" (κακια), in describing what we are redeemed from. We're redeemed from every thing we've done that has fallen short (with the acts of obvious evil/malice/depravity obviously included)!
The next part of the verse is πιστος εστιν και δικαιος ινα αφη ημιν τας αμαρτιας, transliterated "pistos estin kai dikaios [h]ina aphe [h]emin tas [h]armartias," which literally says "faithful he-is and just that he-may/should-let-off to-us the failures"
Then, the last part of the verse is και καθαριση ημας απο πασης αδικας, transliterated "kai katharise [h]emas apo pases adikias," which literally says "and may/should-cleanse us from every un-justness."
Another important point is that "[h]omologomen" (avow) is "present active" ("are avowing"), and then both "aphe" (pardon) and "katharise" (cleanse) are aorist, which is indefinite, timeless statement of fact, not action in time. The aorist tense in the Greek doesn't communicate "when" but the state of something that just "is." So, it is a statement of God's faithfulness (πιστος, "pistos") in return for our acknowledgment that we have committed sins, in the fact that he pardons and cleanses us. See this post for more detailed discussion of this.
Here's my paraphrase of 1 John 1:9-10
"If we admit the fact of our sins, then by his faithfulness his pardon and cleansing applies to us. If we deny we've sinned, we call him a liar and his word is not in us."
So, now that I have picked this apart, you see that this doesn't mean a couple of traditional things. It doesn't mean that you must go to a Roman Catholic priest at Sunday mass and give him a list of the week's specific sins, so that he can grant you remittance for them on God's behalf. That is because Jesus paid the price and God has pardoned them.
It also doesn't mean the typical protest-ant reform-ed alternative to the Roman Catholic Church, where you must go to a priest-substitute-person (like a Christian brother) and confess some specific sins to him, so that God will remit them. That is because Jesus paid the price and God has pardoned them.
It doesn't even mean that every time you "fail" you must perform some ritual verbal confession to man or God, on a case by case basis, not missing any "fault," lest you be condemned. That is because Jesus paid the price and God has pardoned them.
The point is just that we must say the "same thing" that God does about sins: We did commit them, they are unacceptable, and Jesus paid the price in our place to pardon them.
To "avow/acknowledge sins" here is in a general sense. It would preclude any heresy that claims that we have not sinned.
That is why the very next verse, 1 John 1:10 says, "If we should be saying that we have not sinned, we are making him a liar, and his word is not in us."
The problem in translating Greek to English is that we have no aorist verb tense in English, as they did in Greek.
The "aphe" (pardon) and "katharise" (cleansing) are just fact. They apply to us if we "are avowing" the fact that we have sinned. They don't apply if we aren't.
If you acknowledge that you have sinned, the pardon and the cleansing apply to you. If you do not acknowledge that you have sinned, the pardon and cleansing don't apply. In the latter case, by not acknowledging that you have sinned, you must also reject that Jesus paid the price, or else you believe that he paid the price in vain, because there was nothing to pay for if you did not sin. In that case, you are not a believer.
Throughout the Old and New Testaments, people have always been saved by faith. This has not changed. What has changed is that now we look back at how the price was paid 2000 years ago and understand the timeless fulfillment of what Jesus did for us.
Here's something else I thought to do, which is to back-translate from English back to Greek what some people are saying it says:
In 1 John 1:9, what if the aorist αφη "aphe" ("pardon") and καθαριση "katharise" ("cleanse") were not aorist, but future active? In that case, how would it have been spelled in the scriptures?
The answer is:
"αφησει" "aphesei" (future active, 3rd person, singular)
"καθαριει" "kathariei" (future active, 3rd person, singular)
"καθαριει" is actually in Heb 9:14 "...will cleanse our consciences..."
I couldn't find another occurrance of the verb conjugated "αφησει" exactly, but I found the same thing in the 2nd person ("you" instead of "he") in Luke 17:4 where Jesus says "and if seven times in the day he should sin against you and seven times he should return to you saying 'I repent,' you-will-forgive ("αφησεις") him. God has forgiven, therefore we must (always in the future) forgive.
So, the scripture could have said God "will pardon and will cleanse" if that was the intention. But it wasn't, and that's not what it says!
For those unfamiliar with the Koine Greek aorist tense, it cannot be directly and unambiguously translated into English (since we do not have such a verb tense), but I can easily illustrate.
Suppose we were talking about music, and I said,
"I play the piano."
Grammatically, that is the English simple present tense, but the contextual intention is aorist.
I'm not saying that I played the piano yesterday, or that I had been playing it before that, or that I am playing it right now, or that I have been playing it for a couple of hours now, or that I will play it tomorrow, or that I will have played it for a couple hours by the time I have finished doing so. I am just stating a fact, which I could re-phrase as "I am a piano player."
So, you see, the people who misread this verse are like those wondering when I last played it, wondering if I will play it today or tomorrow, and wondering what they have to do to get me to go over, sit at the piano, and play it again, when I've said none of those things. I just said, "I play the piano" (meaning, "I am a piano player.")
When did God last pardon and cleanse us? Do we wonder if he will pardon and cleanse us today or tomorrow? What do we have to do to get him to pardon and cleanse us again? 1 John 1:9 says none of those things. It refers to the fact that God "pardons and cleanses us."
I grant this work to the public domain.