# It came about

"It happened." This phrase marks the beginning of a new part of the story.

# in the fourth year of Jehoiakim ... king of Judah

Jehoiakim had been king of Judah for more than three years. See Jeremiah 25:1. 

# that this word

This phrase refers to the message that follows.

# to Jeremiah

It is not clear why Jeremiah is referring to himself by name here.

# he said

"Yahweh said"