ἐν τούτῳ γινώσκομεν ὅτι ἀγαπῶμεν τὰ τέκνα τοῦ Θεοῦ, ὅταν τὸν Θεὸν ἀγαπῶμεν καὶ τὰς ἐντολὰς αὐτοῦ τηρῶμεν.

1. ἐν
   in
2. τούτῳ
   this
3. γινώσκομεν
   we know
4. ὅτι
   that
   because
5. ἀγαπῶμεν
   we love
   we should love
6. τὰ
   the
7. τέκνα
   children
8. τοῦ
   of the
   the
9. Θεοῦ
   God
10.  
    ,
     
11. ὅταν
    whenever
    when
12. τὸν
    the
13. Θεὸν
    God
14. ἀγαπῶμεν
    we love
    we should love
15. καὶ
    and
16. τὰς
    the
17. ἐντολὰς
    commandments
18. αὐτοῦ
    his
19. τηρῶμεν
    we keep
20.  
    .
     

By this we know that we love the children of God, when we love God and keep his commandments.