It's where the hilt of Tyrael's sword landed in Wortham - from its landing point there, it seems to have tumbled into the water and then been dredged up by one of the Wortham fishermen.
One of the lore items - Priest's Contemplations, Part 1 - explains further.
One of the men retrieved a strange artifact in his nets. It looked like the hilt of an ancient blade, but I know it must be more. The fisherman argued with me, but I convinced him to leave it in the safety of the chapel. A holy place for a holy relic.
Verrall, Priest of Wortham
There are similar craters where you obtain the two shards of the sword at the Khazra Den and the Drowned Temple - and where you find the Fallen Star himself, of course - bringing it all together neatly.