[bike800]

But a valid question that needs to be answered. Even Luther was dismayed at the rampant, wild interepretations that occurred because of his teachings ... You can’t say that “only the Bible is true, and everything needed for salvation is found in scripture alone, when the bible itself doesn’t ever say that. Once that is acknowledged ... Then the question of the marks of the true church can be sought

[aMorePerfectUnion]

“You can’t say that “only the Bible is true, and everything needed for salvation is found in scripture alone, when the bible itself doesn’t Say that.”

Only the Scriptures are inspired by God and hold the final authority for this reason.

Everything necessary for eternal life is found in Scripture.

Everything necessary for maturity of a believer is found in Scripture.

[boatbums]

But a valid question that needs to be answered. Even Luther was dismayed at the rampant, wild interepretations that occurred because of his teachings ... You can’t say that “only the Bible is true, and everything needed for salvation is found in scripture alone, when the bible itself doesn’t ever say that. Once that is acknowledged ... Then the question of the marks of the true church can be sought

Oh, really? Why don't you cite what Luther had to say about his "dismay" because of his teachings? There is a site http://beggarsallreformation.blogspot.com/2016/08/luther-people-are-now-possessed-with.html that posts Luther's thoughts and preaching about those who falsely use grace as a license to sin - something Paul dealt with in his time. In every case where someone implies Luther "regreted" his teachings, those who claim so never post his words in context and they misconstrue what he said. Case in point:

We must certainly receive this message eagerly and gratefully, by it becoming more pious and godly. Unfortunately there's the opposite side, that by this teaching the world becomes more and more hostile, wicked, and malicious; yet not through fault of the teaching but of the people, thanks to the pernicious devil and death. Today people are possessed by seven devils, whereas before it was only one. The devil now bulldozes the people so that even under the bright light of the gospel they become greedier, slyer, more covetous, crueler, lewder, more insolent and ill-tempered than before under the papacy. Why so? Not through fault of the teaching but because the message is not met with thankful acceptance; people cast it to the wind and pay more attention to money and goods than to the blessed treasure which our Lord Christ brings to us. Hence our Lord God scolds again, saying, Have you no appreciation for this—that through the suffering and death of my only begotten Son I have removed your sin and death? Well, then, if that's the way you want it, I will multiply sin and death sevenfold for you. And whereas before one devil possessed and troubled you, now seven worse devils will afflict you. No station in life—peasant, burgher, aristocrat—is spared, from highest to lowest, as they give their lives shamelessly, carelessly to greed, gluttony, drunkenness, immorality, and all manner shameful depravity.

 12. Therefore I exhort that you listen eagerly and lovingly to the Word, receive it with deep gratitude, and beseech the Lord from the bottom of your heart for a firm faith to cling to this teaching. You may be certain that this will bear fruit day by day, as you become more humble, obedient, loving, chaste, and godly, for it is in the nature and art of this teaching to create godly, decent, obedient and pious people. But if people refuse to receive it with loving ready hearts, they will become seven times more wicked than before they came to know this teaching, as experience shows. Be forewarned therefore; the hour is coming—it cannot be avoided—the ingrates will be afflicted and punished. They will then receive what now they have earned. God will certainly find them out [The Complete Sermons of Martin Luther Vol. 5, (Grand Rapids: Baker Books, 2000).  p. 29-30.

There are other examples as well. There will ALWAYS be people who misinterpret the gospel to their own nefarious ends. It doesn't change the fact that the gospel never changes and anyone who would know the truth will find it in God's sacred inspired word - whether through hearing it taught or studying for himself. No man is in authority over God's word but is subject to it and a servant of the truth.

The claim that Scripture doesn't say "only the Bible is true, and everything needed for salvation is found in scripture alone" is a false construct. It ignores the many, many places we are told that it is the Divinely-inspired Scriptures which are able to make one wise unto salvation through faith which is in Christ Jesus. That it is profitable for doctrine, for reproof, for correction, for instruction in righteousness: so that the man of God may be complete, thoroughly furnished unto all good works. (II Timothy 3:15-17). Paul warned, "Do not go beyond the things which have been written— in order that you might not be puffed-up, one on behalf of the one against the other." (I Cor. 4:6) Jesus disputed every false challenge of satan in the wilderness by "it is written". This and many other examples IN Scripture prove that it IS the source of all truth concerning our faith. Whatever men may produce to teach the truth must be backed up the word of God.