This detail is meant to emphasize the fact that the capture of the ark is the real tragedy of the day, not so much the battle defeat and the deaths of Eli’s sons.1 Just like the temple would not serve to protect Israel from judgment (Jeremiah 41:5; Jeremiah 7:12, Jeremiah 7:14; Jeremiah 26:6, Jeremiah 26:9) the ark would not ensure battle victory.2
18 As soon as he mentioned the ark of God, Eli fell over backward from his seat by the side of the gate, and his neck was broken and he died, for the man was old and heavy. He had judged Israel forty years.