Why is love for fellow believers important in Christianity?

In Christian theology, love for fellow believers is a vital indicator of one's spiritual state and relationship with God. As highlighted in 1 John 3:14, a believer 'will know' they have truly passed from death to life by their love for others. This love not only fulfills Christ's command but also serves as a proof of one's regeneration by the Holy Spirit. A lack of love, conversely, signifies a person abiding in death. Therefore, love becomes both a command and a marker of genuine faith, emphasizing the relational aspect of salvation that binds the community of believers together as they reflect Christ's love.