which you are saying

Here "you" is plural. These words could refer to 1) Jeremiah and those with him, or 2) all the people. (See: rc://en/ta/man/translate/figs-you)

It is given into the hand of the king of Babylon

Here "hand" means power or control. This can be translated in active form. Alternate translation: "Yahweh has given it to the king of Babylon" or "Yahweh has given the king of Babylon the power to rule it" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-activepassive)