I have written to you, fathers, because you know him who is from the beginning. I have written to you, young men, because you are strong, and the word of God remains in you, and you have overcome the evil one.

 His object in writing is that they may not sin. There is a two-fold connection of thought here--with what has gone before and with what comes afterwards. There is a two-fold danger that they may indeed think lightly of sin. 