Critics of the New Testament sometimes make reference to this text from Colossians in their attempts to prove that books of the Bible have been lost. What can be said regarding the Apostle Paul's epistle to the Laodiceans? Skeptics have brought up a letter which bears that name.
This nineteen-verse letter is essentially a collection of short excerpts from the canonical Pauline writings. It does not contain any new teachings. It does not contain any new commandments from God. It does not contradict anything found in the New Testament. It does not negatively impact Scripture. The writing style is by no means exceptional. In short, this letter is completely harmless. It does not alter the message of God.
Most scholars believe that this Letter to the Laodiceans was originally written in Latin during the fourth century. In other words, it is generally regarded as a forgery. The textual basis for it is poor. No Greek copies of the New Testament contain it. The church father Jerome made mention of this letter and considered it to be a counterfeit document. It was never widely thought of as inspired Scripture.
As to why this fraudulent letter was written, all that we can really do is speculate. It does not qualify as a lost book of the Bible. But what about the circulated letter that Paul spoke of in Colossians 4:16? Some have identified it to be either Ephesians or Philemon (which is quite a reasonable solution). Whatever the case, we can rest assured that God has given to us everything He wanted us to have. The absence of a book written by an apostle or prophet does not necessarily mean that the Bible has been corrupted.