One building you can point at: a stone church on a corner, with a door, a bell, and people walking in on Sunday morning. Kirk can be thought of as the northern way of saying that same building. Once the word has that building in it, it can also stand for all of them together, and for the national church those buildings belong to.
kirk 的畫面可以想成轉角那棟教堂：石頭牆、一扇門、一口鐘，星期天早上有人陸續走進去。它跟 church 指的是同一個東西，只是蘇格蘭和英格蘭北部的人習慣這樣說。有了這棟建築的畫面之後，這個字還可以往外撐開一層——從一棟，變成這些教堂背後的那整個教會。
From the word’s history
The evidence traces kirk to Northern Middle English kyrke, possibly from Old Norse kirkja, beside Old English ciriche, which became church. The two words are relatives that grew up in different parts of the island.
資料顯示 kirk 來自中古英語北方的 kyrke，可能與古諾斯語 kirkja 有關；而 church 走的是古英語 ċiriċe 這條路。兩個字是同源的親戚，只是在島上不同地區各自長大，所以今天一個聽起來像蘇格蘭，一個是通用說法。
Wiktionary, "kirk"