One of the main things John talks about in 1 John is that knowing God changes you.
First, he insists that it does change you. He is so confident in this that he makes statements about how if you do see certain changes, then you do not know God. There are two main changes: love for others and obedience to the commands of God.
When you come to know God, you also come to love others. If you lack love for others, you do not know God.
Anyone who claims to be in the light but hates his brother is still in the darkness.
1 John 1:9
We know we have passed from death to life, because we love our brothers. Anyone who does not love remains in death.
1 John 3:14
Dear friends, let us love one another, for love comes from God. Everyone who loves has been born of God and knows God. Whoever does not love does not know God, because God is love.
1 John 4: 7-8
However spiritual, wise, or true something may seem, we know that if it does not lead us to love others, then it does not come from God. We know that if we grow in our knowledge of God, we must also grow in our love for others.
Obedience to the commands of God is a second change that is inseparable from knowing God.
We know that we have come to know him if we obey his commands. The man who says "I know him," but does not do what he says is a liar, and the truth is not in him.
1 John 1:3-4
Interestingly, John connects loving others and obeying God's commands, almost as if they are not two distinct things but rather one.
And this is his command: to believe in the name of his Son, Jesus Christ, and to love one another as he commanded us.
1 John 3:23
And he has given us this command: Whoever loves God must also love his brother.
1 John 4:21
This is how we know that we love the children of God: by loving God and carrying out his commands. This is love for God: to obey his commands. And his commands are not burdensome...
1 John 5:2-3