The subject matter of this second letter is very similar to the first. The writer is preoccupied with the truth. He's so stuck on it that he instructs believers not to welcome or greet those who are actively against truth.
And, like 1 John, he reminds them of an old command (1 John 5:3), love one another.
I am continually impressed with how love and truth come together. They first meet in the person of Jesus, who is both truth (John 14:6) and love (John 14:15). In that way Jesus embodies the very essence of healthy relationships. Relationships cannot endure without both love and truth. No wonder he is the way to have a relationship with God! The content and flavor of Christian conversation is love and truth(Ephesians 4:15).