This talk has to do with understanding how metta practice develops concentration. Metta practice also sometimes exposes challenging states of mind that we learn to be more mindful of within the safe and gentle container of LovingKindness.
There is a certain kind of energy required to actually do the sitting/walking schedule of an intensive retreat, which we learn how to cultivate. We also can learn how to relax our energy around our
moment-to-moment experience, which produces a great balance in our practice.