Of whom thou art afraid - The Chaldaeans. Ebed-melech apparently looked forward with much alarm to the b oodshed sure to take place at the storming of the city.
Matthew Henry
Concise Bible Commentary
Here is a message to assure Ebed-melech of a recompence for his great kindness to Jeremiah. Because thou hast put thy trust in me, saith the Lord. God recompenses men's services according to their principles. Those who trust God in the way of duty, as this good man did, will find that their hope shall not fail in times of the greatest danger.
SDA Bible Commentary (limited)
Volume 1-7
17. I will deliver thee. Because of his loyalty toward Jeremiah, God promises the Ethiopian that his life will be spared from “the hand of” the princes of Judah, who were angered by his action regarding the prophet (ch.38:7-13), and that he will “not fall by the sword” (ch.39:18) of the Babylonians, since Jeremiah will undoubtedly intercede for him.