Good News Translation begins with the quote frame “The people reply” to indicate a change in speakers here. Other languages may find this helpful. As noted above, the speakers are probably the disciples of the prophet (or servant), and they are addressing their fellow Judeans in exile in Babylonia.

Who has believed what we have heard?: This rhetorical question appears to say that nobody has believed what the speakers have heard. However, the context suggests it is an exclamation that expresses amazement at certain recent events. The news that the speakers have just heard is so amazing that people find it hard to believe. Good News Translation expresses this question well with “Who would have believed what we now report?” (similarly Revised English Bible). It may be rendered as a strong statement by saying “Whoever would have believed what we have [just] heard!” (see also the third example below). The pronoun we is probably inclusive, referring to the speakers and their fellow Judeans in exile.

And to whom has the arm of the LORD been revealed?: This rhetorical question is parallel to the previous one and also functions as an exclamation. It expresses great surprise at the way in which God has shown his power. No one has seen him act so powerfully. The arm of the LORD is a figure of speech for Yahweh’s powerful action (see the comments on 51.9; see also 52.10). Good News Translation uses an alternative image, saying “the LORD’s hand.” Revised English Bible renders it nonfiguratively with “the power of the LORD.” God’s powerful display here probably refers to the events concerning his servant in 52.13-15 and 53.2-12. The passive verb has … been revealed can be expressed as an active one with Yahweh as the agent; for example, the question may be rendered “For whom has the LORD shown his power?” or “And who has seen how the LORD has acted here?” For languages that prefer a strong statement for this rhetorical question, see the third example below.

For the translation of this verse consider the following examples:

• Has anyone believed what we have [just] heard?
To whom has Yahweh’s power [just] been demonstrated?

• Who would believe what we have heard?
Who is it that the LORD has shown such power to?

• Nobody would believe what we have just heard!
Nobody has seen the LORD’s power so revealed!

Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .