There has been much debate through the centuries of church history over Paul’s "lost epistle to the Laodiceans." The biblical reference for the "lost epistle" comes from Colossians 4:16: "And when this letter has been read among you, have it also read in the church of the Laodiceans; and see that you also read the letter from Laodicea. " There are two ways to interpret this verse: either Paul is referring to a letter written by the Laodicean church to the Colossian church, or he is referring to a letter he personally wrote while in Laodicea.
The most obvious interpretation, however, supported by both the context and grammatical considerations, is that Paul wrote a letter to the church at Laodicea at the same time that he wrote the one to the church at Colossae. The problem is that no letter addressed to the Laodiceans has been preserved in the Pauline corpus.
At various times in history, the church has attempted to resolve the mystery of the Laodicean epistle. One approach was to recreate the epistle. A "pseudepigraphical" Epistle to the Laodiceans has survived in a Latin translation and had some acceptance in the Western Church into the Middle Ages. Another approach has been to identify the epistle with one of Paul’s New Testament epistles. Both Ephesians and Philemon have been identified as the missing epistle by church historians, although neither argument has gained wide acceptance.
Regarding the hypothetical premise posed by this discussion question, what if the missing letter was discovered and authenticated by archaeologists today? Should it be included in our New Testament Canon?
The first test of canonicity lies with the writer. Is the writer a true prophet–or spokesman–of God? Obviously, if the letter was authenticated as being written by the Apostle Paul, it would meet this requirement, many books in our New Testament testify. Even by his own contemporaries, Paul was recognized as an apostle and a spokesman for God (cf. 2 Peter 3:15-16). However, not every word Paul wrote was inspired Scripture, and his authorship by itself would not qualify the supposed document as Scripture.
Another factor to be considered is the church’s acceptance or recognition of the document in history. Throughout church history, there has been near unanimous agreement regarding the canonicity of the 27 books of the New Testament. Unlike the Old Testament Books of the Apocrypha , which has been a source of controversy and serious debate, the Pseudepigraphal writings of the New Testament have been universally rejected by all traditions of the church. This is important because it is the church that must discover and authenticate a writing as inspired Scripture, not archaeologists.
In summarizing his argument why a letter like "the epistle to the Laodicians" should be rejected, Geisler states:
None of the New Testament Apocrypha have experienced more than a local or temporary acceptance. Most have enjoyed at best a quasi-canonical status, merely appended to various manuscripts or listed in tables of contents. No major canon or church council accepted them as part of the inspired Word of God. Where they were accepted into the canon by groups of Christians it was because they were believed wrongly to have been written by an apostle or referred to by an inspired book (for example, Col. 4:16). Once this was known to be false they were rejected as canonical.
Therefore, a discovery of this letter should be rejected due to the historic determination of the church considering this supposed letter.
 Geoffrey W. Bromiley, The International Standard Bible Encyclopedia, Revised (Wm. B. Eerdmans, 1988; 2002), 3:74.
 Norman L. Geisler, Baker Encyclopedia of Christian Apologetics, Baker reference library (Grand Rapids, Mich.: Baker Books, 1999), 36.
 Ibid., 35.
 Ibid., 36.