Speech and silence

From Carlyle's 1830 notebook: "Speech is human, silence is divine, yet also brutish and dead: therefore we must learn both arts."

Splendidly muddled construction! I suppose he means that we need to learn both speech and silence; but it looks as though we need to learn both brutishness and death; and indeed that speech characterises the brute and the dead. The barking of a dog; the mutter of the grave.