Sacred Blood

The sacredness of the king's blood is the central idea of the opening of this play.

Mowbray hesitates to answer the charges against him, because his accuser is a close relation of the king. (Bolingbroke is Richard's "father's brother's son," as Richard describes it.) But "setting aside his high blood's royalty, and let him be no kinsman to my liege, I do defy him" (I.i.58ff.)

Bolingbroke, for his part, is willing to "lay aside my high blood's royalty." He does not want any special treatment in the judging of his accusation, but claims to accuse Mowbray "in the devotion of a subject's love" (I.i.31).

Richard assures Mowbray that he will be an impartial judge, not showing Bolingbroke any preference on account of their shared blood:

Mowbray, impartial are our eyes and ears:
Were he my brother, nay, my kingdom's heir,
As he is but my father's brother's son,
Now, by my sceptre's awe, I make a vow,
Such neighbour nearness to our sacred blood
Should nothing privilege him, nor partialize
The unstooping firmness of my upright soul:
He is our subject, Mowbray; so art thou:
Free speech and fearless I to thee allow.

Richard not only assures Mowbray, but vows "by my sceptre's awe" to be impartial in judgment.

In this speech, Richard makes a distinction between his blood and Bolingbroke's. They both share the blood of Edward III, by different father's, but only Richard's blood is "sacred"--because only Richard is in the line of descent to be king. Bolinbroke's blood has "neighbor nearness" to Richard's, but that is all. He is "but my father's brother's son."

This establishes an important point of the play: Richard is the only person who has the right to be king, whatever his faults may be. The only legitimate king is the person who has the sacred blood of a king. It does not matter that Bolingbroke or Gloucester might make a better king, because no matter how capable they are or how near they are to the king in blood, only Richard has the sacred blood of a king.