Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
They brought it into the house of Dagon (see the marginal reference) in order to enhance the triumph of the gods of the Philistines over the God of Israel. (Compare Sa1 31:9; Jdg 16:23; Isa 37:12.)
This custom still existed among the worshippers of Dagon so late as the reign of Josiah (see the marginal reference).
Emerods - A corruption of "hemorrhoids." It is mentioned Deu 28:27 among the diseases with which God threatened to punish the Israelites for disobedience.
The "lords" (see Jdg 3:3) were very unwilling to give up their triumph, and, with the common pagan superstition, imagined that some local bad luck was against them at Ashdod. The result was to bring the whole Philistine community under the same calamity.