“I see no evidence in Scripture that only Scripture is authoritative. “
God has established authorities in the home, church, and government. There are also natural laws that teach us. And in any organization someone has to be in charge and becomes the “authority” for those who choose to be part of it.
But there is no authority higher than God’s word. He created the Heavens and earth by His word. Christ is the Word incarnate. Anyone trying to exercise authority above God’s word is in rebellion.
Who should people obey when these “authorities” direct doing things contrary to the Bible?
Acts 5:29
But Peter and the other apostles answered and said: “We ought to obey God rather than men.”
Here are the verses you referenced:
1 Corinthians 11:2
Now I praise you, brethren, that you remember me in all things and keep the traditions just as I delivered them to you.
2 Thessalonians 2:15
Therefore, brethren, stand fast and hold the traditions which you were taught, whether by word or our epistle.
Who established these traditions? The apostles. There is a difference between traditions of men and traditions of the apostles. Notice that these traditions were also by “epistle”. That is, they were transmitted by the New Testament scriptures. At the time of this writing, the New Testament was incomplete. Obviously the church traditions were implemented orally until they were written. This is one of the reasons Peter specifically gives for writing his epistles (i.e. letters).
To introduce a tradition after the apostles were dead, or to change a tradition of the apostles, is to actually fail to keep the tradition of the apostles. The Catholic church is among those who claim to exert apostolic authority, but we see from several passages in the New Testament that apostolic authority could be falsified and must be tested. No one today has such authority. Peter, Paul, James, John and other apostles are still with us in their apostolic authority today. It is found in their writings which are scripture.
John 15:20
Remember the word that I said to you, ‘A servant is not greater than his master.’ If they persecuted Me, they will also persecute you. If they kept My word, they will keep yours also.
Galatians 1:11-12
But I make known to you, brethren, that the gospel which was preached by me is not according to man. For I neither received it from man, nor was I taught it, but it came through the revelation of Jesus Christ.
2 Peter 1:12-15
For this reason I will not be negligent to remind you always of these things, though you know and are established in the present truth. Yes, I think it is right, as long as I am in this tent, to stir you up by reminding you, knowing that shortly I must put off my tent, just as our Lord Jesus Christ showed me. Moreover I will be careful to ensure that you always have a reminder of these things after my decease.
Matthew 15:3
He answered and said to them, “Why do you also transgress the commandment of God because of your tradition?”
Mark 7:8
For laying aside the commandment of God, you hold the tradition of men —the washing of pitchers and cups, and many other such things you do.
He was quoting from this passage when He said it:
Isaiah 29:13
Therefore the Lord said:
“Inasmuch as these people draw near with their mouths
And honor Me with their lips,
But have removed their hearts far from Me,
And their fear toward Me is taught by the commandment of men”
Isaiah also had this to say about such people who prefer manmade religion over the word of God:
Isaiah 8:20
To the law and to the testimony! If they do not speak according to this word, it is because there is no light in them.
The Church has preserved Apostolic Tradition. Furthermore, the Scriptures make no claim that Scripture alone is authoritative, and so to assert the doctrine of Sola Scriptura is to assert a doctrine that contradicts itself.
http://orthodoxinfo.com/inquirers/tca_solascriptura.aspx
Therefore, brethren, stand fast and hold the traditions which ye have been taught, whether by word [i.e. oral tradition] or our epistle (II Thessalonians 2:15).
The word here translated “traditions” is the Greek word paradosis — which, though translated differently in some Protestant versions, is the same word that the Greek Orthodox use when speaking of Tradition, and few competent Bible scholars would dispute this meaning. The word itself literally means “what is transmitted.” It is the same word used when referring negatively to the false teachings of the Pharisees (Mark 7:3, 5, 8), and also when referring to authoritative Christian teaching (I Corinthians 11:2, Second Thessalonians 2:15). So what makes the tradition of the Pharisees false and that of the Church true? The source! Christ made clear what was the source of the traditions of the Pharisees when He called them “the traditions of men” (Mark 7:8). Saint Paul on the other hand, in reference to Christian Tradition states, “I praise you brethren, that you remember me in all things and hold fast to the traditions [paradoseis] just as I delivered [paredoka, a verbal form of paradosis] them to you” (First Corinthians 11:2), but where did he get these traditions in the first place? “I received from the Lord that which I delivered [paredoka] to you” (first Corinthians 11:23). This is what the Orthodox Church refers to when it speaks of the Apostolic Tradition — “the Faith once delivered [paradotheise] unto the saints” (Jude 3). Its source is Christ, it was delivered personally by Him to the Apostles through all that He said and did, which if it all were all written down, “the world itself could not contain the books that should be written” (John 21:25). The Apostles delivered this knowledge to the entire Church, and the Church, being the repository of this treasure thus became “the pillar and ground of the Truth” (I Timothy 3:15).
The testimony of the New Testament is clear on this point: the early Christians had both oral and written traditions which they received from Christ through the Apostles. For written tradition they at first had only fragments — one local church had an Epistle, another perhaps a Gospel. Gradually these writings were gathered together into collections and ultimately they became the New Testament. And how did these early Christians know which books were authentic and which were not — for (as already noted) there were numerous spurious epistles and gospels claimed by heretics to have been written by Apostles? It was the oral Apostolic Tradition that aided the Church in making this determination.