Strengthen the weak hands, and make firm the feeble knees: The prophet gives two commands here to the people of Judah to strengthen themselves in preparation for God’s coming. He is not commanding a third party to strengthen the people. If this is not clear, translators may say “Strengthen your weak hands….” The imagery of weak hands and feeble knees refers to weakness caused by fear (compare Ezek 7.17; 21.7; Nahum 2.10). The prophet is telling the people to be courageous and not to be afraid as they prepare for God’s arrival. For languages that do not use these images for fear, see the examples below.

This brief verse reads literally “Strengthen the weak hands and the feeble knees make firm.” The Hebrew syntax has the following chiasmus: verb > noun phrase > < noun phrase < verb. The function of this structure is to draw special attention to the call for courage. Translation examples for this verse are:
• Take courage and be strong;
you who are weak, stand firm.

• You who are feeling weak,
have courage and stand resolute.

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 .