I write to you, fathers, because you know him who is from the beginning. I write to you, young men, because you have overcome the evil one. I write to you, little children, because you know the Father.
John extended his declarations further, mentioning two of the three sub-classifications again, that is, the fathers and the young men; but, in this case, the two groups stand for all three.  Paul also mentioned three charismatic gifts in  1 Corinthians 13:8, making the three stand for all nine mentioned in  1 Corinthians 12:8-10.  John did a similar thing in the next verse.