II Corinthians 2:17
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.
Paul and those with him did not corrupt the Word of God. There were many others who were corrupting and twisting God’s Word to achieve their own selfish goals, but Paul and those with him were speaking God’s Word with sincerity, genuineness, and pure motives. They kept in mind that they were speaking it in the sight of God.
I Thessalonians 2:4
But as we have been approved by God to be entrusted with the gospel, so we speak, not as pleasing people but God, Who proves our hearts.
They understood that they had been approved by God to be entrusted with the gospel, so their main concern was pleasing God by speaking the gospel faithfully, and not corrupting it or watering it down. We want to be like that too!