In the Parable of the Sheep and the Goats (Matthew 25:31-46), what is the defining characteristic that separates the 'sheep' from the 'goats' in the final judgment?

A Their adherence to strict religious rituals and practices. B Their public displays of piety and charitable giving. C Their acts of compassion and service towards the 'least of these'. D Their unwavering faith and belief in the teachings of Jesus.