Literature: Isaiah ties this portion of the prophecy to verse 1 with parallel phrasing. First, Yahweh commanded him to write with a “man’s hand.” Now, Yahweh speaks “with a strong hand.” The reference in both cases is to the power of Yahweh’s message.
Culture: The combination of a reference to speaking “with a strong hand” is an unusual combination in English. In the cultural world of the Mediterranean, the two are tied together by their conceptual representations. Bruce J. Malina describes the way that the body was used in metaphors:
The main framework of perimeters or boundaries of this interaction between the individual and the world outside the individual is described metaphorically, for the most part, using parts of the human organic whole as metaphors. Thus, most obviously, man is endowed with a heart for thinking, along with eyes that fill the heart with data; a mouth for speaking, along with ears that collect the speech of others; and hands and feet for acting. More abstractly, man consists of three mutually interpenetrating yet distinguishable zones of interacting with his environments: the zone of emotion-fused thought, the zone of self-expressive speech, and the zone of purposeful action.
When Isaiah tells us that Yahweh speaks with him, the mouth is the representative of the communication from the Lord. The hand, however, is the metaphor for purposeful action. When Yahweh speaks with “a strong hand,” those words should be understood to require action.
Scripture: In verses 9 and 10, Isaiah has condemned Judah’s current policy. Now he announces that Yahweh requires him to take a different path that his people.