Paul writes, “After this letter has been read to you (καὶ ὅταν ἀναγνωσθῇ παρ᾿ ὑμῖν ἡ ἐπιστολή), see that it is also read in the church of the Laodiceans (ποιήσατε ἵνα καὶ ἐν τῇ Λαοδικέων ἐκκλησίᾳ ἀναγνωσθῇ) and that you in turn read the letter from Laodicea (καὶ τὴν ἐκ Λαοδικείας ἵνα καὶ ὑμεῖς ἀναγνῶτε)” (Col 4:16; NIV).
This verse gives us a nice example of ellipsis; ἐπιστολή is not repeated but assumed in the final clause. τὴν modifies the unexpressed ἐπιστολήν.
It gives us another example as well of how we often write in short-hand and expect the reader to understand the missing parts. If you just read the final phrase, who wrote the second letter? The NIV’s “the letter from Laodicea” sounds like the church in Laodicea wrote a letter to the Colossian church. However, most people (if not all) understand that this second letter was written by Paul to the Laodicean church, and he wanted to make sure that his letter was also sent to Colossae.
If Paul had taken the time to write all the words to be precise and not confusing, he may have written τὴν ἐκ Λαοδικείας ἐπιστολήν μου or perhaps τὴν ἐπιστολήν μου τῷ Λαοδικείᾳ.