Callous disregard for the life of another sentient being prevents spiritual progress, because it is based on the assumption that we are somehow more important, and our lives more valuable, than our human ‘enemies’ or non-human animals.
Simply put, it is NOT possible to attain full enlightenment while continuing to exploit and kill other sentient beings (human and non-human) for our pleasure or convenience.
As Dharma practitioners, we must remedy our lapses in observing and proclaiming the First Precept —Protect Life— including our shameful silence on war, abortion, capital punishment, gross economic inequality (which leads directly and indirectly to uncountable deaths from malnutrition, disease, domestic violence, and crime), and the slaughter of animals for food and sport.
The Buddha said: “Right conduct leads to absence of remorse; absence of remorse leads to happiness; happiness leads to concentration; and concentration is the condition of liberation from suffering.”
Without Right Conduct, firmly grounded on the First Precept, there can be no liberation from suffering.