As for you, the anointing which you received from him remains in you, and you don't need for anyone to teach you. But as his anointing teaches you concerning all things, and is true, and is no lie, and even as it taught you, you will remain in him.
So, first of all, he just says, "You've overcome the wicked one." Now he gives you the secret of their strength and how it is that they overcame the wicked one. "I write unto you, young men, because you are strong, because God's Word abides in you." And that is always our strength against the enemy. None of us are immune from the attacks of the enemy. I don't care how far you progress in your spiritual experience and your relationship with God. You will, as long as you are in this body, not be immune from Satan's attacks. You never grow beyond temptation, in fact, many times the more you grow, the greater is the temptation that the enemy lays before you. You never grow beyond the point of being tempted. You never grow beyond the point of struggling with the enemy, being in conflict with Satan. But, "I write unto you, young men, because you are strong, because the Word of God abides in you." And that's the secret of my strength in overcoming the enemy is the Word of God abiding in my heart. "Thy Word," David said, "have I hid in my heart, O Lord, that I might not sin against you" ( Psalms 119:11 ). The power of the Word in my heart against temptation, against sinning against God.