So then, brethren, stand firm and hold to the traditions which you were taught, whether by word of mouth or by letter from us. [2 Thess 2:15]Let's take a moment to examine what Paul is discussing.
First, let's talk simply about the logic behind the use of this passage - namely, that the word "traditions" here is used to support traditions known by some churches as they know those traditions today. It is ironic that many will argue 2 Timothy 3:16, when it says "all scripture," does not refer to Paul's epistle or any other New Testament work, yet they will argue here that Paul's use of the word "traditions" refers to all tradition in toto. Yet many traditions today in most "apostolic" churches can be proven to either have developed over time or to have come at a much, much later date, so that Paul would have had absolutely no idea of them at the time. Many will argue that these traditions are keeping in line with the mentality or spirit Paul would have had, but the problem is that Paul specifies who received these traditions and from whom they came: these are the traditions "which you were taught," and were taught "by word of mouth or by letter from us." These were traditions given to the Thessalonians, and received directly from the apostles. Any traditions outside of this context could not be relevant and, by extension, could not be "apostolic."
Even if, for the sake of argument, we were to extend the "you" to the universal church, the context of "traditions" would still be limited to that which the apostles themselves gave directly, and any traditions not given directly by the apostles would be irrelevant to the passage. To use the verse to support post-apostolic traditions or traditions that came hundreds of years later - be it the bodily assumption of Mary or the various liturgies - would be erroneous. One cannot logically expand "traditions" to all traditions after the life of the apostles the way one can expand "scripture" in 2 Timothy 3:16 to the New Testament - God continued writing scripture even after Paul died; Paul did not continue giving traditions after he died.
Second, let's look at the full context within scripture. Paul has just begun a request regarding "the coming of our Lord Jesus Christ" (v. 1), that the Thessalonians should "not be quickly shaken from your composure or be disturbed either by a spirit or a message or a letter as if from us" (v. 2). After a lengthy discussion of the false teaching that Christ's return is coming soon, the apostle writes:
But we should always give thanks to God for you, brethren beloved by the Lord, because God has chosen you from the beginning for salvation through sanctification by the Spirit and faith in the truth. It was for this He called you through our gospel, that you may gain the glory of our Lord Jesus Christ. So then, brethren, stand firm and hold to the traditions which you were taught, whether by word of mouth or by letter from us. [2 Thess 2:13-15]The "traditions," within their proper context, have a two-fold definition: they are referring to eschatology specifically, and the Gospel generally. Paul is warning the Thessalonians about false teachings regarding the coming of Christ, hence they are to keep the "traditions" (or "teachings" as the NIV translates) that the apostles gave regarding it, and they are to hold fast to the Gospel, in which those traditions are part. The Gospel the apostles preached was one of repentance and coming to Christ who, through saving faith, would restore us body and soul on the day of resurrection. The latter part was what troubled the Thessalonians, as they were beginning to argue and worry over when the second coming and resurrection would happen. These are the "traditions" which they are told to stand fast in - not a liturgy, not extra-biblical stories, not prayer to the saints - but the Gospel of Christ and the expected day of resurrection and judgment.
In fact, this section has an indirect relation to Paul's words in the first epistle he sent them:
We give thanks to God always for all of you, making mention of you in our prayers; constantly bearing in mind your work of faith and labor of love and steadfastness of hope in our Lord Jesus Christ in the presence of our God and Father, knowing, brethren beloved by God, His choice of you; for our gospel did not come to you in word only, but also in power and in the Holy Spirit and with full conviction; just as you know what kind of men we proved to be among you for your sake. You also became imitators of us and of the Lord, having received the word in much tribulation with the joy of the Holy Spirit, so that you became an example to all the believers in Macedonia and in Achaia. [1 Thess 1:2-7]Note, again, the focus of this section of scripture: the Gospel. It was the Gospel which was delivered "not...in word only" but also "by word of mouth," the Thessalonians receiving "the Holy Spirit with full conviction." These are the "traditions" which the apostles gave the Thessalonians - and indeed, the universal church - by word of mouth and by letter. There was nothing new or hidden that was given to the Thessalonians - what was given to them was exactly what was given to Paul by Christ, and which Paul proclaimed throughout all of Asia Minor.
To read into the word "traditions" here as any unwritten tradition is not only erroneous (as previously established), but likewise comes close to robbing the Gospel of its glory. It is reading the modern context of a word backwards into an older use, and a use which refers not to the practices of man but the teachings of God. When we are told to "stand firm" in strong language denoting hope and inspiration (not mere remembrance and repetition), what other context could it mean but the Gospel, in which we "may gain the glory of our Lord Jesus Christ"? It was against an attack of these traditions - the Gospel and all it entailed - that Paul warned the Thessalonians to guard against. This is why he warned them not to be shaken in their faith "by a spirit or a message or a letter as if from us," just as he warned the Galatians to hold anyone who preaches a Gospel contrary to that which they were likewise taught "by word of mouth or by letter" to be accursed (cf. Gal 1:8-9).
Let us, therefore, follow the command of Paul and "stand firm and hold to the traditions" of the apostles - not empty ritualistic traditions, but rather the great tradition that Christ died to redeem us from our sins and in us is the hope of the coming resurrection. Of that day no man knows, but one thing is certain: those whom are God's sheep will never be lost, for no man can snatch them out of His hand. Who is greater than God? In these traditions, let us all stand firm. Amen.