Rashi on the Prophets and Writings

and officers of the king They were jealous of him that he took a high position.

to bring to the house of the Lord When they left home, they were unaware of the destruction of the Temple, and en route, they heard of it, and rent their clothing and shaved their beards.
and having cut themselves An expression [denoting] laceration.

through Gedaliah Heb. ביד, [lit. by the hand of Gedaliah]. Since he should have heeded the counsel of Johanan the son of Kareah, and he did not heed, Scripture accounts it for him as though they had been slain by him.

by the great waters [By the pool of great waters.]

in Geruth Chimham In the sojourning place that David gave to Chimham the son of Barzilai the Gileadite when he returned from the war of Absalom, as it is stated in the Book of Samuel (II 19: 39): “Chimham shall go over with me.”