Sacrifice, the Imperium is built on it. The sayings are all true. The Blood of Martyrs is the seed of the Imperium. The Loyal Slave Learns to Love the Lash. Only in Death does Duty End. 

For ten thousand years we have endured, sometimes we have thrived, other times merely survived. For a hundred centuries we have fought and died, spilt the blood of our enemies and our own over an uncountable number of battlefields. Mankind has sacrificed itself, for itself, so that it might last for another generation, and another, and another. Those sacrifices are for no greater cause than for the acts themselves. It is done in the unspoken hope that some day, perhaps in another ten thousand years, a generation will live without sacrifice and mankind's destiny is fulfilled for eternity.