The constant factor that accompanies all mental states and activities is awareness- the ground of citta. Citta gets conditioned by sankhara of intention, attention and contact. Widening past these we return to awareness.
This talk introduces the four heavenly abodes (Brahma Viharas), their relationship to one another, they're near and far enemies and a range of motivations for practice. The second half of the talk is dedicated to the practice of compassion, the second of the four Brahma Viharas