3 ideas
The essence of tea is nothing more than boiling water, making tea, and drinking it; everything beyond that is ornament that risks becoming the point. A small grass-hut room with plain utensils removes the distractions of wealth and display, so host and guest meet the bare act directly. The practice aims at a Buddhist-inflected state of sufficiency, not aesthetic refinement pursued for its own sake.
The text sets out exact measurements and placements for utensils, shelves, charcoal and the room, often keyed to yin-yang counts on the daisu stand. It also states that once the rules are fully internalized, the practitioner abandons them and acts freely without violating their spirit. On this view rules are scaffolding for embodying a principle, and discarding them before mastery is simply ignorance.
Rikyū's ideal of wabi is illustrated with a poem by Ietaka: someone waiting only for flowers should see spring already present in grass sprouting through snow in a mountain village. The lens redirects attention away from conspicuous beauty and toward nascent life latent in scarcity and austerity. Poverty and emptiness become places where the most vital quality is found, not deficits to overcome.