The poem is a short, blunt reflection on what happens when words lose their force. Its title, "Speaking truth to power," sets up a familiar idea: that honest speech can challenge those in charge. The poem then undercuts it. The opening lines are a little tangled, but they seem to say that anyone who pays attention to the lies "expressed on all occasions now" can see that lying has become so constant and so open that it is no longer an art. There is no skill or subtlety left in it.
The second stanza turns colder. "Guns hear nothing / whether in earnest or not" suggests that weapons don't respond to sincerity, argument, or even honesty. Truth may be spoken, but force doesn't listen.
The speaker sounds weary and disillusioned, perhaps quietly angry. The mood is bleak and stripped down, and the short lines leave a sense of silence after them, as if speech itself has run out of room.