What: “the things that,” as in verse 27.
Low is the opposite of “noble birth” (Good News Bible “high standing”) in verse 26 and means “lowly-born” or “from an unimportant family.”
Despised is the most common meaning of the following Greek word, which in 6.4 Good News Bible translates “of no standing.” This Greek word is related to the word for “nothing.” Paul may be thinking of this when he adds even things that are not. Similarly, the following phrase means “in order to destroy the things that (the world thinks) are (something).” The words in parentheses are implied. “Something” means “something important.” This way of understanding despised becomes clear if the UBS Greek text is followed. The first part of the verse may be translated “and God has chosen what the world considers as lowly-born and despises (x) things that do not exist.” Other manuscripts add “and” at the point marked (x). But the omission of “and” suggests not only that the same group is being spoken about, but also that the two phrases, before and after (x), mean essentially the same thing.
The last part of the verse is translated clearly by Die Bibel im heutigen Deutsch “… for he [God] wanted to reduce to nothing those who are something before men.” Another way of saying this is “He [God] decided to cause people whom humans consider important to have no importance at all.”
Quoted with permission from Ellingworth, Paul and Hatton, Howard A. A Handbook on Paul’s First Letter to the Corinthians, 2nd edition. (UBS Handbook Series). New York: UBS, 1985/1994. For this and other handbooks for translators see here .
