"Thrice is he armed that hath his quarrel just,
And he but naked, though locked up in steel,
Whose conscience with injustice is corrupted,"

says Shakespeare. But not only does a clear conscience give power; it also gives light. With it we could sit at the center of the earth and yet enjoy the sunshine. Without it we live in a rayless prison.

He that has light within his own clear breast
May sit i' the center, and enjoy bright day:
But he that hides a dark soul and foul thoughts
Benighted walks under the midday sun;
Himself is his own dungeon.

John Milton.