'Strong' in the Bible

I have written to you, little children, because you have known the Father. I have written to you, fathers, because you have known the one who has existed from the beginning. I have written to you, young people, because you are strong and because God's word remains in you and you have overcome the evil one.

This is how we will know that we belong to the truth and how we will be able to keep ourselves strong in his presence.