Apparantly God's Providence seen that it was not part of Scripture.
Well, let's be fair here. Bible is the word you may be looking for: "God's providence saw that it was not part of the Bible." Bible is from Latin biblia ('books'; biblioteca is Spanish for 'library'), but Scripture refers specifically to holy, God-inspired writings. It appears apparent that there are Scriptures (holy, God-inspired writings) that did not make it into the Bible (the 'books' as in biblia). Jude quotes Enoch, and the writers of the Books of Samuel, Chronicles, and Kings referenced other books written by prophets and men of God that didn't make the canon.
To say that Paul wrote a whole letter that was un-inspired and then wrote two inspired ones is a stretch. Firstly, Paul said several times in 1Cor. that some of the things he commanded were from him and others from the Lord. If he wasn't 'fully inspired' when he wrote 1Cor. 14, when was he fully inspired? It becomes rational, however, when you differentiate 'Bible' from 'Scripture' (after all, many God-inspired proclamations in Bible times didn't make it into the Bible): man comprised the former (Bible), and God issued the latter (Scripture). Apparently, not all holy
Scripture was recorded for us in the
Bible; but in the Bible, we still have everything we need with nothing missing.