SN 10.4 Manibhadda Sutta: With Manibhadda
A kind of ‘spirit’ called a ‘yakkha’ says to the Buddha that one who practices mindfulness has everything improve and that they overcome animosity. It cures everything! The Buddha replies that only one who practices metta/loving-kindness can overcome animosity.
Concentration alone doesn’t get you there, in other words, head and heart together are needed.