What Paul spoke was theopneustos, it wasn't merely a hospitable greeting, but divine truth.
You shouldn't be so quick to disregard the word in perhaps a bias against OSAS.
Notice also it is Christ who brings this work to completion in his people, not they themselves. Here is John Gill on this matter concerning the text:
"Wherefore by it is undoubtedly meant the work of grace upon their hearts, sometimes called the work of faith, because that is a principal part of it: this is God's work, and not man's, as may be concluded from the nature of the work itself, which is the transforming of a man by the reviewing of him, a regeneration, a resurrection, and a creation, and therefore requires almighty power; and from the condition man is in by nature, he is dead in sin, and has no power to act spiritually, and much less what is equal to such a work as this; he has no will, desire, and inclination to it, but all the reverse; and if he had, he could no more effect it, than the dry bones in Ezekiel's vision could cause themselves to live. This is the work of God."
Compare this text with Philippians 2:11-13 and we see the same truth expanded. This is also witnessed in Hebrews 12:2, and expresses the same truth. Ezekiel 36:27 also expresses this same truth which Scripture Paul knew, and was totally aware of.
You probably need to read some more Bible, compare passages that are similar, and implement 2 Timothy 2:15 because this truth is expressed all over its precious pages to Soli Deo Gloria.
To take your error to its logical end, using the verse in context since it is Christ accomplishing this in them, Christ will then not finish what he began.