21 I did not write to you because you do not know the truth, but because you know it, and because no lie is of the truth.
1 John 2:21 Cross References - CAB
Proverbs 1:5
5 For by the hearing of these a wise man will be wiser, and a man of understanding will gain direction;
Proverbs 9:8-9
Romans 15:14-15
2 Peter 1:12
12 Therefore I shall not neglect to constantly remind you concerning these things, although you know and have been established in the present truth.
Jude 1:5
5 But I want to remind you, though you once knew this, that the Lord, having saved the people out of the land of Egypt, afterward destroyed those who did not believe.