The following comments are from Navigator's and Quiet Time Diary journals. One verse will be entered, then the comment, then the date.

v. 4    I have no greater joy than this, to hear of my children walking in the truth.

    John is referring to children which are his spiritual children - in this case Gaius, who he was writing to. I'm sure that believers who have led others to the Lord Jesus (I'm not sure if I have) also feel compassion for their new "children." This brings discipleship to mind. (DRM 7/14/06)

v. 7, 8    For they went out for the sake of the Name, accepting nothing from the Gentiles. 8Therefore we ought to support such men, so that we may be fellow workers with the truth.

    Since we know that the Name is Jesus, I would interpret this to be a suggestion that we support people who go out to serve the Lord Jesus; like missionaries and pastors and Christian workers of similar work. Depending on the size of the "church" that they are serving, they probably don't have much, or any, additional income. (DRM 1/9/09)

v. 9    I wrote something to the church; but Diotrephes, who loves to be first among them, does not accept what we say.

    It seems that there is always a non-Christian critic. Here it seems that Diotrephes is the critic who wants to create problems. In the full paragraph (v.10), John intends to speak to the church about the problem. I wonder how I (you) would deal with the problem of this man in the church? (DRM 1/10/09)

v. 10    For this reason, if I come, I will call attention to his [Diotrephes] deeds which he does, unjustly accusing us with wicked words; and not satisfied with this, he himself does not receive the brethren, either, and he forbids those who desire to do so and puts them out of the church.

    Diotrephes opposed John's messengers sent to the church - we don't know the location of the church.
    This verse shows the problem John had with Diotrephes. The man was clearly hindering the spreading of the gospel message.
    It seems that we all have critics on what we believe as Christ followers. We have to pray for God=Jesus' guidance on what to say or not to say to these people. No matter what they say, we are to stand on the word of God - the Bible - and what it says. The critics need to know this. (DRM 5/6/16)

v. 11    Beloved, do not imitate what is evil, but what is good. The one who does good is of God; the one who does evil has not seen God.

    I know some good non-Christians. They seem kind and compassionate, but their words eventually show their heart is not on serving the Lord Jesus. I pray that my words will show others my love for Christ, and cause them to know Him personally also. (DRM 7/15/06)

v. 12    Demetrius has received a good testimony from everyone, and from the truth itself; and we add our testimony, and you know that our testimony is true.

    This makes me think of a job recommendation. Demetrius is not otherwise mentioned in this letter, and this verse is right after stating that 'good' is from God.
    Clearly John recommended Demetrius for what he was doing and wanted Gaius to know that he (John) supported what he (Gaius) was doing. (DRM 9/11/12)

v. 13, 14    I had many things to write to you, but I am not willing to write them to you with pen and ink; 14but I hope to see you shortly, and we will speak face to face.

    John's letter to Gaius (v. 1) was like a father to a child - or at least a younger person. In these verses he tells Gaius why the letter is so short.
    Writing makes things more clear and can be re-read often. (This has been preserved nearly 2, 000 years.) Talking to someone in person is less permanent, but can refer to things that don't need to be public. There are advantages for both.
    We don't know what John told Gaius in person, but it was likely more about Diotrephes and his accusations about the church (v. 10) (DRM 12/29/13)