The connector so begins the main clause that completes the comparative sentence beginning with “As” in verse 14 (see the comments there). Just as the servant’s appearance shocked many people, so now many nations and their kings will be shocked and surprised at what they see happening to him. However, it is not clear what causes their astonishment. Is it the wretched condition of the servant described in verse 14, or is it his exaltation referred to in verse 13? Revised English Bible rearranges the contents of verses 14-15, and clearly supports the first interpretation. Good News Translation, Bible en français courant, and Die Bibel im heutigen Deutsch favor the second one with their renderings. However, most translations leave some ambiguity in verse 15. The most likely understanding is that the nations and their kings are astonished at the servant’s exaltation rather than at his disfigurement.

So shall he startle many nations: The Hebrew verb translated startle has a primary meaning of “sprinkle” (New International Version). Hebrew Old Testament Text Project prefers the sense of “purify” for this verb here. It may refer to some unusual cultic or ritual action. However, Hebrew Old Testament Text Project considers startle to be an alternative meaning of the verb as well. It is the choice of most modern versions and is supported by the Septuagint, so we accept that this verb has the wider sense of “astonish/startle/astound” here. The servant will astonish the nations because of his exaltation (or because of his frightening appearance). Many nations refers to a great number of the nations, if not all of them (see the comments on many in the previous verse). Bible en français courant says “the crowd of nations.”

Kings shall shut their mouths because of him uses idiomatic language to indicate that world rulers will be speechless, unable to say anything because they are so astonished at what they see concerning God’s servant. If this idiom is translated literally, it might simply indicate that the kings will close their mouths, so it is important that the meaning be made clear. Good News Translation provides a useful model with “and kings will be speechless with amazement.” The phrase because of him indicates that the servant is the cause of the kings’ astonishment. As noted above, it is unclear whether it is because of the way he looks, or whether it is because of what is about to happen to him.

For that which has not been told them they shall see is the first of two clauses that give the reasons for the astonishment of the nations and their kings. They will witness an event that is totally new and surprising.

And that which they have not heard they shall understand is parallel to the previous line. The nations and their kings will also come to understand something they had never known of before. Bible en français courant has “what they hear/understand is something [previously] unheard of.” Good News Translation combines this line with the previous one, saying “They will see and understand something they had never known.” Neither one of the explanatory clauses specifically mentions what the nations and their kings will see and understand. However, we presume that they refer to the statements made about the servant in either verse 13 or 14. Their reaction to these unheard of events will be one of utter amazement, similar to their reaction to the physical appearance of the servant.

For the translation of this verse consider the following examples that complete those for the previous verse respectively:

• … so now he will amaze many nations;
kings will be speechless on his account;
because they will see something that they have never been told about,
and will come to understand something they have never heard before.

• But now he will astonish many nations;
kings will be unable to speak about him;
for they will witness things they have never been told,
and will understand things they have never heard before.

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 .