革 is a flayed hide spread flat — the radical of everything leather. 圭 lends its sound. Shoes were leather goods first: hemp sandals for summer, hide boots for war, silk slippers for courts, but the character kept its leather soul.
Shoes off at the door is non-negotiable in Chinese homes — expect house slippers handed over at the threshold. And never gift shoes to a partner: 送鞋 sounds like sending someone to 邪 (evil) or walking away — superstition says they'll use the shoes to leave you.
Leather 革 cut precise as a jade tablet 圭 — a well-made SHOE.
合脚的鞋 'a shoe that fits' is the standard metaphor for a good marriage — 鞋合不合脚，只有自己知道: only the wearer knows.