What does it mean that Paul was not "corrupting" the word of God in 2 Corinthians 2:17?
It means Paul did not water down, adulterate, or peddle God’s Word like a huckster selling inferior goods. He did not hawk a diluted spiritual product for personal gain; rather, he spoke with sincerity, as from God, in God’s sight, and in Christ, defending his apostleship against false teachers.
Les connects the word “corrupt” in 2 Corinthians 2:17 back to Isaiah chapter 1, where the same word is used. Les explains that Paul pictured corrupting the Word as selling a product likened to wine watered down with water—an adulterated spiritual product. Paul refused to act like a huckster hawking wares worth less than the price he charged. Many people do corrupt or hawk the Word of God as an adulterated product, but Paul says he did not do that; he came in complete sincerity, as of God, in the sight of God, and spoke in Christ. Les emphasizes that Paul was defending his apostleship: he was not like the false teachers, but was bringing the absolute truth. The kind of false teachers Paul had in mind, Les says, are described in Jude, perhaps as good a description as can be found anywhere in Scripture.
For we are not as many, which corrupt the word of God: but as of sincerity, but as of God, in the sight of God speak we in Christ.