Every Christian throughout the ages is a part of the body of Christ—united in the gospel: one body, one Spirit, one hope. We are all under the Father's sovereign care and are called to eagerly do the hard work "relationally" to maintain the unity that is a fact spiritually. So much to be thankful for. We are one in Christ!
Paul appeals to the Corinthians to walk in unity. Pride was creating factionalism in the Corinthian church. Humility was the answer; a humility that embraces the ugliness and offense of the cross. In the face of the cross and the gospel there is no room for our pride, because they highlight that we have nothing good in ourselves.
The ninth commandment forbids perjury in a courtroom context, but its implications cover our speech in general and, especially, our speaking of others. God wants a people who treasure truth and who also treasure and guard the unity of his church.