Christian love is both vertical and horizontal. It begins with love for God. This love starts in us by our "obeying the truth" of the Gospel. The resulting new birth purifies us from the inside out. This love originates and ends in God. We love Him only because "he first loved us" (1 John 4:19).
The horizontal love is harder. Someone described two porcupines needing warmth from each other on a cold night--"They needed each other; even though they needled each other." We sometimes feel the same way. But Peter calls us to a love that is sincere (genuine, without hypocrisy), deep (fervent, constant), and from the heart (the center of our emotions, desires, and will).
Maybe today there is another believer who has not received a sincere, deep, and heartfelt love from you. In fact, maybe they have experienced the opposite. So you really want to follow Jesus? You know what you have to do.
Father, may our love be more than lip service. Make us men and women of action, even when it is hard. In Jesus' name. Amen.