Plainly read: to be "saved" you must "confess" and "believe". Obviously, "salvation by faith alone" is ruled out here. But surely there is a Protestant answer to this, for now it appears Saint Paul has his own "Not By Faith Alone" verse (since we already know Saint James has his own)!If you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto righteousness*, and with the mouth confession is made unto salvation.
Of all the historical Protestant sources I consulted, I think John Calvin gave the most direct answer (the other sources didn't really address it):
John Calvin: With the mouth confession is made unto salvation It may seem strange, that he ascribes no part of our salvation to faith, as he had before so often testified, that we are saved by faith alone. But we ought not on this account to conclude that confession is the cause of our salvation. His design was only to show how God completes our salvation, even when he makes faith, which he implants in our hearts, to show itself by confession: nay, his simple object was, to mark out true faith, as that from which this fruit proceeds, lest any one should otherwise lay claim to the empty name of faith alone: for it ought so to kindle the heart with zeal for God’s glory, as to force out its own flame. And surely, he who is justified has already obtained salvation: hence he no less believes with the heart unto salvation, than with the mouth makes a confession. You see that he has made this distinction, — that he refers the cause of justification to faith, — and that he then shows what is necessary to complete salvation; for no one can believe with the heart without confessing with the mouth: it is indeed a necessary consequence, but not that which assigns salvation to confession. (Commentary on Romans 10:9-10)
Calvin's solution is to say true belief necessarily produces a public profession, proving the faith was genuine. This is very close to how Protestants have traditionally read James 2.
The big question now is: does this claim make sense exegetically? Does it make sense to say "confession" is what "completes salvation" and yet also say it's a only fruit of salvation? That doesn't make sense. Salvation doesn't happen without "confession". And, further, if Paul is speaking about "believing with the heart," clearly already talking about genuine faith, then the issue of needing fruit in the form "confession" to prove the faith genuine makes no sense in this passage. (The term "saved" cannot mean something along the lines of "vindicate" or "show fruit".)
So how can the Protestant get out of this? One Protestant response I've encountered from a few Protestants (not by anyone significant) is that "saved" here is not speaking of saving one's soul, but rather being saved (by God) from earthly persecutions. But this is totally implausible. Paul is clearly talking about saving one's soul, as the context is abundantly clear (see especially Romans 10:11-12), and the fact he uses "saved" once in verse 9 shows the belief and confession must both apply to the same "saved".
One other interpretation I came across is from Protestant apologist Jason Engwer, who wrote an article concerning this very passage, "Does Romans 10 contradict Justification Through Faith Alone?" When he begins suggesting possible interpretations, he says the following:
Are we to believe that a person attains righteousness through faith, but isn't justified yet, then attains justification upon confessing Christ with his lips? That would be a possible way to read the passage, but not the best way.Well, that's quite a concession! He says a "possible way to read the passage" is one that just so happens to deny Justification by Faith Alone! Ok, so there was a slip of the pen; let's pretend he never said that (but certainly keep that interpretation in mind).
Here is what he thinks is the "best way" to read the text:
I believe that the best way to explain the passage is to see the salvation associated with confession as a reference to what's commonly called sanctification, including eschatological vindication. Philippians 2:12 tells us to work out our salvation, even though we're already justified. The term "salvation" can be used to refer to a collection of categories that involve deliverance from sin, including both justification and sanctification.Note that he begins by making the assumed (and fictitious) Protestant distinction between "justification" and "sanctification". For example, he assumes Philippians 2:12 is speaking of sanctification rather than justification, though only the term "salvation" is used. Further, as noted earlier, verse 9 assigns believing and confessing under the single heading of "will be saved," so he cannot have "saved" consist of two different meanings (justification and sanctification).
Turning to the Greek of the text, the term "[will be] saved" in verse 9 is the verb sozo (used in various places, e.g. Eph. 2:8), while the term "salvation" has the same 'save' root but is the noun soteria (used in various places, e.g. Rom. 1:16). (This is where we get the term "soteriology" when speaking on the study of the 'mechanics' of Christian salvation.) Both terms are used numerous times in the NT and are used interchangeably: neither can be forced into the category of justification or sanctification (nor does Paul ever come close to such a thing). *Also, the word improperly translated in some Bible versions of 10:10 as "justified" is actually the Greek noun dikaiosune, which means "righteousness," which is also used numerous times in the NT (with no inherent bias towards justification or sanctification).
This brings up one final question: why is there the distinction between "righteousness" and "salvation" in verse 10? This distinction has to be as real and meaningful as the real distinction between "believing" and "confessing" to which each is assigned. Contextually, the "saved" in v9 could very well be that of "justification," which means two conditions are required, and thus refuting Sola Fide. This means Paul never included "confessing" in the category of "works" which he spoke negatively about earlier in the Epistle. Thus, verse 10 must be speaking of "two stages," or "two events," similar to the first option Jason gave. Whether this believing and confessing are a one time event at conversion or both continuous is irrelevant, but given that confessing is most rationally something that must be done at all times as a Christian implies both are continuous and justification is contingent on both.
Alternatively, if Romans 5:9-10 happens to be related to Romans 10:9-10, then there might be one other possible reading:
Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God. For if while we were enemies we were reconciled to God by the death of his Son, much more, now that we are reconciled, shall we be saved by his life.This is interesting because it shows "justified" (also meaning "reconciled" in this context) is not synonymous with "saved" (which must be something 'bigger') - and clearly Paul cannot be talking about "sanctification" here. Thus, when the Protestant speaks of "justification" (particularly upon conversion), they're projecting too much of salvation into their meaning. Thus, one can be justified but not (yet) saved. This fits perfectly with Romans 10:9-10.
So the Protestant has to pick how they're going to view Romans 9-10: if it is (a) speaking of "justification," then Sola Fide is explicitly refuted, but if it is (b) speaking of a justification-salvation distinction as in Romans 5:9-10, then the Protestant definition of justification is refuted (which is just as serious of a problem).
What is also interesting to note is that one other place where both of the same Greek terms for “believe” and “confess” are used is in John 12:42, “many even of the authorities believed in [Jesus], but for fear of the Pharisees they did not confess it.” In other words, the necessary for two components is confirmed, and clearly someone can believe but not confess, and thus will not be saved, which fits perfectly with the warning of not confessing Jesus before men (e.g. during persecution) and thus being damned (Mat 10:32).