The Buddha addressed the monks gathered at Jetavana at Anathapindika’s Monastery, in Savatthi as follows, regarding the advantages of mettā:
"Monks, eleven advantages are to be expected from the release (deliverance) of heart by familiarizing oneself with thoughts of loving-kindness (metta), by the cultivation of loving-kindness, by constantly increasing these thoughts, by regarding loving-kindness as a vehicle (of expression), and also as something to be treasured, by living in conformity with these thoughts, by putting these ideas into practice, and by establishing them. What are the eleven?
1. "He/she sleeps in comfort. 2. He/she awakes in comfort. 3. He/she sees no evil dreams. 4. He/she is dear to human beings. 5. He/she is dear to non-human beings. 6. Devas (gods) protect him/her. 7. Fire, poison, and sword cannot touch him/her. 8. His/her mind can concentrate quickly. 9. His/her countenance is serene. 10. He/she dies without being confused in mind. 11. If he/she fails to attain arahantship (the highest sanctity) here and now, he/she will be reborn in the brahma-world.”
From the Discourse on Advantages of Mettā, Anguttara Nikaya, 11.16, translated by Piyadassi Thera, and modified for gender inclusivity.