"And so we know and rely on the love God has for us. God is love. Whoever lives in love lives in God, and God in him." NIV translation
We know that God is the very definition of love and so there is no way to separate the two. Therefore, if you are His you will have love in your heart for God. You will also love other people because you know that Jesus loves them and died for them as well as for yourself.
"In this way, love is made complete among us so that we will have confidence on the day of judgement, because in this world we are like him." NIV translation
Love is made complete when it is given and becomes active. For example, if you see a starving person and say I love you but do nothing to help the hunger, you will not be believed. But, if you say I love you and also give the hungry some food, love will be demonstrated and made complete.
If you have that kind of selfless love which only comes from the presence of God in your life, you can be confident even unto death just as Peter was in his second letter.
"There is no fear in love. But perfect love drives out fear, because fear has to do with punishment. The one who fears is not made perfect in love." NIV translation
Through Christ, we know that our sins were punished and we know that our relationship with God was restored. Therefore, we do not fear punishment. Since we do not have to fear punishment from El Shaddai (God Almighty), then we do not need to fear anything or anyone else as He is above all else.
"We love because he first loved us." NIV translation
It is only through our relationship with God and His Spirit living in us that gives us the ability to love anyone but ourselves. In fact, as John said in chapter one, we do not even know what love is until we believe in Jesus Christ.
"If anyone says, 'I love God,' yet hates his brother, he is a liar. For anyone who does not love his brother, whom he has seen, cannot love God, whom he has not seen. And he has given us this command: Whoever loves God must also love his brother." NIV translation
We love God because of what he did for us which we accept by faith (not seeing). In Genesis 1:27, we see that God made man in His image. Therefore, how can we hate the image of God and yet say that we love God? The next time you feel anything less than love for others, remember that they are created in the image of God and that is why we must love them.