A.T. Robertson Commentary 1 John 2:14

"I have written unto you, fathers, because ye know him who is from the beginning. I have written unto you, young men, because ye are strong, and the word of God abideth in you, and ye have overcome the evil one." — 1 John 2:14 (ASV)

I have written (εγραψα). Repeated three times. Epistolary aorist referring to this Epistle, not to a previous Epistle. Law (Tests of Life, p. 309) suggests that John was interrupted at the close of verse 13 and resumes here in verse 14 with a reference to what he had previously written in verse 13. But that is needless ingenuity. It is quite in John's style to repeat himself with slight variations.

The Father (τον πατερα). The heavenly Father as all of God's children should come to know him. He repeats from verse 13 what he said to "fathers." To the young men he adds ισχυρο (strong) and the word of God abiding in them. That is what makes them powerful (ισχυρο) and able to gain the victory over the evil one.