What does 2 John 1:4 mean?

Verse 4 begins the main body of John's letter and is also the general theme of the text: John's joy at finding truth in the lives of some of the "children." John is pleased at the growth of the believers in the church to which he writes. His use of the term "greatly" emphasizes his tremendous elation. This was news John had either heard or, more likely, had personally encountered. His joy was specific, relating to children walking in obedience to the truth of the gospel. This verse is also similar to 3 John 1:4, which also mentions John's happiness at seeing Christians live according to their faith. These two letters (2 John and 3 John) were probably written to a different audience, but share many similarities. This strengthens the case that the apostle John wrote both.

John then connects this obedience to its source, which is the command of God. This letter frequently references the Father-Son relationship within the Trinity. The introduction mentioned the Father and the Father's Son (2 John 1:3). Verse 9 will mention the teaching of both the Father and Son. A believer who trusts in Christ must also believe and obey the teachings of the Father.