What gives Ichabod an excuse to visit Katrina at her house?

Ichabod was invited to a "quilting frolic" at Katrina's home.

It was suddenly interrupted by the appearance of a negro in tow-cloth jacket and trowsers, a round-crowned fragment of a hat, like the cap of Mercury, and mounted on the back of a ragged, wild, half-broken colt, which he managed with a rope by way of halter. He came clattering up to the school door with an invitation to Ichabod to attend a merry-making or “quilting frolic,” to be held that evening at Mynheer Van Tassel’s; and having delivered his message with that air of importance, and effort at fine language, which a negro is apt to display on petty embassies of the kind, he dashed over the brook, and was seen scampering away up the hollow, full of the importance and hurry of his mission.