For which I am an ambassador in bonds: that therein I may speak boldly, as I ought to speak. An ambassador in bonds - An ambassador being the representative of his king, his person was in all civilized countries held sacred. Contrary to the rights of nations, this ambassador of the King of heaven was put in chains! He had however the opportunity of defending himself, and of vindicating the honor of his Master. See above.
As I ought to speak - As becomes the dignity and the importance of the subject.