What does 1 Corinthians 1:5 mean?

Paul is writing a letter that will focus heavily on correcting wrong actions and attitudes among the Christians in Corinth. Still, he begins by giving thanks to God for them. He has made clear that they are already sanctified in Christ (1 Corinthians 1:2) and have received God's grace in Christ (1 Corinthians 1:4).

Now Paul adds that God's grace to these Christians in Corinth included being made rich in Christ in all speech and all knowledge. The word "speech" as used here may refer to speaking in tongues by the power of the Holy Spirit, something Paul will deal with at length later in his letter. Or, he may have in mind the idea of "speaking well:" being able to express ideas about Christ clearly and articulately. Such skill in communication was highly valued in the Greek and Roman culture of the day.

In addition, by God's grace and in Christ, the Christians in Corinth had been made rich in knowledge. Paul likely means they understood much about the things of God as he—Paul—had taught them during his time with them. In other words, they really "got it." Because of God's gift of grace to them, they truly understood and retained all the meaningful ideas Paul had passed on to them.

However, as this letter will later make clear, being rich in speech and knowledge does not always translate to being rich in love and faithfulness to God. Still, these are things Paul thanks God for giving to them.