Further the well-being of all. Being ethical safeguards the well-being of one's own soul, which is immortal. If we understood correctly the great cosmic laws, this would not be a question for us. The greatest of cosmic laws is that of reincarnation. Souls don bodies again and again until their earthly incarnations are complete.
Love is the law of the Earth plane.
We come from spiritual worlds of love and unity into the physical world of fear and separation, and our task is to overcome our fear and learn to live in love. Simply, because Spirit is Love, and has created a universe in Love beneficial to every creature within it. Fear has destroyed the balance. Whatever you do to others will be done to you, if not in this life-time, then in another. It is all very simple, that is the law of the universe.