This refers to to the servants that he had sent to Hezekiah with a message. This can be stated clearly. Alternate translation: "In the messages you sent with your servants" (See: [[rc://en/ta/man/translate/figs-explicit]])
Here Sennacherib speaks of himself conquering many things. He is actually conquering them with the armies and chariots that he commands. Alternate translation: "We have gone ... We will cut ... we will enter" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
Here the word "fruitful" refers to the forest being dense and full of healthy trees. The understood information may be supplied. Alternate translation: "and into its most fruitful forest" (See: [[rc://en/ta/man/translate/figs-ellipsis]])