1 John

We can so easily slip into the idea that knowing God means something mental, something intellectual. But John makes it clear "We know we have come to know (God) if we keep his commandments (1 John 2:3)."
He goes on to elaborate: "If I say I know God and do not keep his commands I am a liar and the truth is not in me." Another: "I one says he abides (knows like a friend) ought to walk in the same manner as He walked (1 John 2:6)." And then the more positive: "Whoever keeps His word, in him the love of God has truly been perfected (completed). Bu this we know we are in Him." This a life conformed to the example of Christ.
John uses three different ways to say the same thing, to inforce his point: know him, abide in him, simply in him. We have to know him to walk as he walked. That requires observing God's behavior, his demeanor, his attitude. We learn those things by abiding.
John loves to keep the tension. He speaks of new commands and old commands. What command does he mean? He never exactly explains. He assumes his readers will know.
"Beloved, I am not writing a new commandment, it is an old commandment. This old commandment is the word from beforehand. What does John mean here? He says it is from the beginning. What beginning? The beginning of time or the beginning of their relationship? "You heard it from the first." What command is that?
Then John says, "on the other hand I write a new commandment to you." Are the new and old one and the same? Are they two sides of the same coin?
The new command has to do with light. Light is a favorite metaphor of John's. The light is shining brighter and brighter. It seems the darkness is passing away.
I think John is saying you obey the old commandment which is to abide in God and live as Jesus lived. As you do that you are more and more changed into the likeness of God. The light is an image. You are a light to a needy and sinful world. You see into the darkness better as you come to experience God's wisdom. You are growing in faith and holiness as you are obedient to Him.