You may also hold that, despite the fact that Protestants misinterpret (or misunderstand) a divine truth revealed by God, they can still be united to Christ and thus be saved. Hence, there is a basis for cooperation between Catholics and, at the least, Evangelicals. If you hold this, then please consider the following:
First, a misinterpretation of divine truth is still, by definition, error. It is still a failure to affirm and believe a truth which God has revealed as necessary for belief. This objective fact must never be ignored.
Second, by misinterpreting a divine truth revealed by God one does so either intentionally (i.e., conscious rejection of divine truth) OR accidentally (i.e., unintentional rejection of divine truth). There are no other options.
I will presume for the sake of argument that you hold that the person who is the conscious rejector of divine truth shall be damned, and the person who unintentionally misinterprets what God has revealed can still enter heaven and who will have all his misinterpretations and misunderstandings straightened out.
If you hold this, in either case you must admit that, if the unintentional misinterpreter goes to heaven and the intentional misinterpreter goes to hell, then Truth still does not really matter. Why?
BY THE VERY FACT THAT BOTH STILL HOLD SOMETHING WHICH IS FALSE, AND BOTH FAIL TO BELIEVE THE TRUTH!
This is the objective fact of both examples. Yet both end up in eternally opposite places! The objective fact that both did not believe the truth, then, is not the determining factor in their eternal fates. Please think this through... This contradicts what God has declared when, through St. Paul, He made it clear that those who do not believe the truth will be judged and condemned (2 Thes.2:12).
To hold the above can ONLY mean that Truth does NOT, in fact, matter; and since Jesus is the Truth, it means Jesus does not matter for salvation. (It would also necessarily mean that faith -correct faith- does not matter.) It means that only intentions matter because BOTH of these persons failed to actually believe the Truth before they died.
Therefore, you MUST conclude that to hold this means that man is saved by his own intentions. This is none other than a gospel of works. It is the heresy of salvation by works. (Any act of body, mind or will is a work.) It is well known that liberal "Catholics" hold this heresy, but any Protestant (this includes Evangelicals, Pentecostals, and fundamentalists) who holds such is guilty of the damnable heresy of salvation by works.
Jesus did not say he who misinterprets revealed truth, even though he does not believe, will still be saved. Rather, Jesus declared without qualification, "He that believes and is baptized shall be saved; but he who does not believe shall be condemned" (Mk.16:16).
Jesus is concerned with objective reality, -whether we actually believe the truth or not- for there is no subjective circumstance which He cannot overcome. To hold that there is, is to deny God's omniscience and omnipotence. Here's why:
1) Since nothing is impossible with God (Lk.1:37), there is nothing
which he can not foresee and no circumstance in which He can not overcome.
2) Since God promises that He will reward those who seek Him (Heb.11:6),
and
3) since God desires ALL men to come to know the truth (1 Tim.2:4),
there is nothing which would keep God from revealing His truth to those
who are open to it (Jn.18:37) and who sincerely seek it (Mat.7:7f). Only
bad will can do this.
Therefore, we must conclude that if someone does not know and believe in the dogmas of the Catholic Church before they die (including those who misinterpret the truth), they are either not open to the truth and not sincerely seeking it OR they are rejecting truth when made aware of it. As a result of the above promises, no one could "sincerely" misinterpret God's truths up till the day they die, for Christ promised that we shall know the truth (Jn.8:32). Ignorance of the Truth, then, is due to the individuals own fault of ultimately not being open to the Truth.
St. Thomas Aquinas recognized this truth when he stated in his Summa Theologica (I-II, q.84, art.4, ad 5; II-II, q.53, art.2, ad 2) :
All sins which are due to ignorance can be reduced to sloth, to which pertains the negligence of a man who declines to acquire spiritual goods because of the labor associated with them... Since knowledge is further removed from morality than prudence,... it follows that ignorance has the nature of mortal sin, not of itself, but on account either of a preceding negligence or the consequent result, and for this reason ignorance is reckoned one of the general causes of sin... All sin proceeds from some ignorance.
In dealing with this same subject, Pope St. Pius X (1903-14), forcefully declared that:
We pray and conjure you to reflect on the ruin of souls which is wrought
by this single cause: ignorance of those most sublime truths, so far beyond
the natural understanding of the multitude, which must nonetheless be known
by all men alike in order that they may attain eternal salvation... We
positively maintain that the will of man can- not be upright nor his conduct
good while his intellect is the slave of crass ignorance!... If, as a result
of ignorance, lack of faith is added to corruption, the situation scarcely
admits of remedy, and the road to eternal ruin lies open. This we solemnly
affirm: the majority of those who are condemned to eternal punishment fall
into this everlasting misfortune through ignorance of the mysteries of
the faith which must necessarily be known and believed by all who belong
to the Elect.
("Acts of the Supreme Pontiff Pius X," Vatican Press, Rome, 1904.)
Misinterpretation is still, in effect, ignorance of truth, and ignorance is ultimately due to sin.
With the true nature of misinterpretation exposed, there is another fatal problem for those who think that the person who misinterprets God's revealed Truth until his death can still be united to Christ and thus still be saved. It concerns, again, God's attributes. If God were to make exceptions by allowing those who misinterpret his revealed truths to be saved, then, God would be making an exception with one of His attributes and its necessary consequences. Remember, to truly believe in God is to believe His attributes can never be separated from Him.
It must be recognized that even those who end up "unintentionally" misinterpreting what God has revealed none-theless still, objectively speaking, do NOT believe the Truth. If these could still be saved in such a state, then, God makes an exception with His attribute of Truth. But this cannot be. God cannot make any exceptions with His attributes. If He did, then God would be denying one of His own attributes. But this would mean that God would, in fact, be denying Himself. By definition of what is meant by "God," this is an absolute impossibility. God can NEVER deny Himself (2 Tim.2:13).
Thus, we MUST conclude that God cannot make an exception when it comes to both His Truth and the absolute necessity for those who would be saved to believe in His revealed truths. Again, as God and His attributes are one and indivisible, and as Truth is an attribute of God, and thus is identified with God and cannot be divided, we MUST hold that to be saved one must believe in ALL that God has revealed.
Those who believe God makes exceptions for the "unintentional" misinterpreter of His truths end up holding by conse-quence that God must deny Himself to do such. This would make them, by definition, atheists. It must be held by any person of reason (and reason and faith can never contradict each other) that if the necessary consequences of a belief or position were to lead to a denial of God and truth, then the belief itself is false and damnable for those who hold it. The truths revealed by God MUST be held in their entirety or they will be of no benefit to those who hold only some of them. This is so because divine truth is indivisible.
By the fact that Evangelicals in particular, and Protestants in general, reject certain truths revealed by God, the truths they do profess will be of no avail to them. Pope Leo XIII (1878-1903), in his encyclical Satis Cognitum (On the Unity of the Church: June 29, 1896), spelled this out clearly:
such is the nature of the faith that nothing can be more absurd than to accept some things and to reject others. If, then, it be certain that anything is revealed by God, and this is not believed, then NOTHING WHATEVER is believed by divine faith... But he who dissents even in ONE POINT from divinely-revealed truth absolutely rejects ALL faith, since he refuses to honor God as the Supreme Truth and formal motive of faith. In many things they are with me, in a few things not with me; but in those few things in which they are not with me, the many in which they are WILL NOT PROFIT THEM... for they who take from Christian doctrine what they please lean on their own judgment, not on faith... and they obey themselves more truly than they obey God." (Capitals added to emphasize point.)
There can be no TRUE ecumenism until the one true God and His revealed truths are acknowledged and believed in their entirety. And there can be no authentic cooperation with those who deny God and His truth. There can only be evangelization and the hope for their conversion.