What is the context?
Diotrephes provides a sharp contrast to Gaius. He loves to be first, rejects the elder’s instruction, speaks maliciously against him and refuses the visiting brothers. He also blocks those who want to receive them and puts them out of the church.
The elder plans to call attention to this conduct if he comes. He then tells Gaius to imitate good rather than evil. The contrast concerns actual conduct: the one doing good is of God, while the one doing evil has not seen God.
Demetrius receives a good testimony from others, from the truth itself and from the elder. He offers a positive example after the warning about Diotrephes. The letter commends his reputation without explicitly telling us his office or saying that he carried it.
How is this passage commonly understood?
Wesley and the USCCB notes see Diotrephes as exercising authority in the community and understand verse 11 as warning against following his conduct. Wesley suggests he may have been its pastor. The USCCB introduction discusses several possible reasons for the conflict. Those reconstructions do not change what the letter states about his slander and exclusion of others.
Wesley understands not having seen God as being a stranger to Him. The warning directs readers to recognize the seriousness of evil conduct and follow the good example commended to them. It gives no procedure here for determining every individual’s final standing before God.
Where does this fit in God's plan?
In Mark 10:42–45, Jesus answers the desire for greatness by calling His followers to serve. He points to His own service and the giving of His life. Philippians 2:1–11 likewise grounds care for others in Christ’s humility. These passages explain why a church leader’s desire to be first conflicts with the pattern Christ gives His people.
What is our position?
Our studies Who Shepherds the Church? and The True Church According to Jesus describe recognized leadership as mature, accountable service among believers. We read the warning about Diotrephes in line with that conclusion: wanting to be first and controlling others conflicts with the kind of care these studies describe.