# the word of Yahweh came to me, saying, 'Do

"Yahweh gave me a message. He said, 'Do" or "Yahweh spoke this message to me: 'Do".  See Jeremiah 1:4.

# where there is mourning

"where people are mourning"

# I have taken away my peace from this people ... and my steadfast love and mercy

"I will no longer act towards them with peace ... or with steadfast love and mercy"

# this is Yahweh's declaration

"this is what I, Yahweh, have declared". Yahweh speaks of himself to express the certainty of what he declares. See Jeremiah 1:8.