Consciousness is the presence of experience. A conscious being does not merely exist as an object; something is happening from that being’s point of view.
This matters because pain, fear, pleasure, hunger, grief, confusion and relief are experiences. If a being can experience suffering, then that being is not morally irrelevant.
Consciousness is difficult to explain fully. Science can study brain processes, behaviour and reports of experience, but subjective experience itself remains a deep question. A reasoned approach should avoid both careless certainty and careless dismissal.
Evidence notes
Evidence for consciousness may include behaviour, nervous systems, learning, communication, pain responses and evolutionary continuity.
Ethical questions
If there is good reason to believe a being can suffer, how should uncertainty affect our treatment of that being?
Conclusion
Consciousness matters because experience matters. Where experience includes suffering, moral concern becomes harder to avoid.