חַזְּק֖וּ יָדַ֣יִם רָפ֑וֹת וּבִרְכַּ֥יִם כֹּשְׁל֖וֹת אַמֵּֽצוּ׃
너희는 약한 손을 강하게 하여주며 떨리는 무릎을 굳게 하여주며
Radak
ראה, an imperative mode; who was this addressed to? This was not addressed to a specific person, but it is a mode of speech addressed to anyone who considers what follows as pertinent to himself. We have a similar usage of the imperative not being addressed to someone specific in Jeremiah 13,18 אמר למלך ולגבירה, as well as in Isaiah 60,6 קול אומר קרא!, “a voice says: call out!” No specific person is addressed by this proclamation. Similarly, in Isaiah 35,3 חזקו ידים רפות. Also in verse 4 of that chapter we encounter a similar construction.