On the feast day commemorating the falling asleep of St. John the Theologian, we listen to a beautiful Epistle reading (1 John 4:12-19) that reminds us of God's boundless, self-sacrificial love. We know that we dwell in this love by the fruit of its Spirit in our lives: "love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, [and] self-control" (Galatians 5:22-23).
But what does it mean to be perfected in this love? And why does perfect love cast out all fear? To be perfected in God's love means to do good without begrudging or resenting anyone, "for [God] makes his sun rise on the evil and on the good, and sends rain on the just and on the unjust" (Matthew 5:45). Perfect love casts out all fear because it is unconditional and irrevocable; in perfect love, there is no longer a concern about losing a reward or failing to live up to God's standards. Perfect love is an unmerited gift, given freely and shared freely.
In other words, perfect love is the law of the Spirit of life in Christ Jesus. "There is therefore now no condemnation for those who are in Christ Jesus. For the law of the Spirit of life in Christ Jesus has set me free from the law of sin and death" (Romans 8:1-2). We don't live anymore oppressed by a selfish desire for rewards or a cravenly fear of retribution. We are free to grow in God's love as much as we desire. It is through this wonderful love that our Lord grants us a merciful heart that beats in harmony with his own heart.
"What is a merciful heart?" St. Isaac the Syrian writes. "It is a heart on fire for the whole of creation, for humanity, for the birds, for the animals, for demons, and for all that exists. By the recollection of them the eyes of a merciful person pour forth tears in abundance. By the strong and vehement mercy that grips such a person’s heart, and by such great compassion, the heart is humbled and one cannot bear to hear or to see any injury or slight sorrow in any in creation. For this reason, such a person offers up tearful prayer continually even for irrational beasts, for the enemies of the truth, and for those who harm her or him, that they be protected and receive mercy. And in like manner such a person prays for the family of reptiles because of the great compassion that burns without measure in a heart that is in the likeness of God."