The Buddha taught that there are 8 ways to cultivate metta, which manifest into 11 benefits. The talk includes numerous stories from around the world, including the story of how the Buddha came to teach lovingkindness.
There is a great release of the contractions of the heart... the past pains, hurts and anguish that we've taken in and taken on as "mine", "me", as"I am". It it's not so easy to relinquish these habituated patterns of our-self. Our commitment to our practice and willingness to take the journey is what affords the transformation. Not so easy at times, but well worth it.