This verse distinguishes two groups, the children of God (for which see comments on 1 John 3.1) and the children of the devil. Verse 9b has indicated the distinctive feature of the first group: a person who does not and cannot sin “is born of God.” The distinctive feature of the second group is given in verse 10b, again by saying what they do not.

By this it may be seen who are…, and who are …: the words by this can best be taken as pointing forward to verse 10b.

It may be seen, or ‘we/people can see clearly,’ ‘it is manifest.’

To emphasize the force of verse 10b, some versions have a slightly adjusted rendering of verse 10a such as “here is the clear difference between God’s children and the Devil’s children:…” (Good News Translation), or “the children of God and the children of the devil are distinguished in this way:….” (Translators’ Translation).

The children of the devil: the phrase parallels “the children of God.” Therefore the renderings of children of should be the same, unless idiom would not allow this, as may be the case in languages that use honorifics. It is worth noting here that John nowhere uses the expression “born of the devil,” or “seed of the devil.”

Is not of God, see comments on “is not of the Father” in 2.16.

Although the preceding clause would seem to have brought the argument to a close, John adds nor he who does not love his brother. This clause serves as a further description of the man who ‘does not do right’ and at the same time forms a transition to the next section.

Some versions transpose one of the clauses in order to get a more easily running sentence; for example, “anyone who does not do what is right, or does not love his brother, is not God’s child” (Good News Translation), ‘no one is (born) of God who does not act righteously, or does not love his brother.’ Others change the last clause into a complete sentence; for example, ‘Whoever does not do right is not of God. Whoever does not love his brother is not of God.’ Such solutions are acceptable, provided that the explanatory function of the second sentence remains clear.

Nor, or ‘and also not,’ ‘equally not’; or ‘thus too,’ ‘similarly.’ For “to love” and “love” (here and in verses 11, 14, 16-18) see comments on 2.10 and 5, and for brother (also in verses 12-17) see comments on 2.9.

Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The First Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .