The letters are different combinations of Kindness, Judgment and Mercy — lines and dots, signifying opening and closure.
Each letter is a specific combination of Kindness, Judgment, and Mercy — the three columns made operational at the executive level.
Op. 13 established that the Sefirot can be viewed as three columns (yosher: Kindness, Judgment, Mercy). Op. 20 takes that structural fact down to the level of individual letters. Each letter is a combination of CHaDaR — the columns operating at the executive level. The chapter sets the terms by which the rest of the book's letter-talk works.
A letter, considered visually, is composed of lines and dots — strokes that open into space, dots that close. Klach reads this visual fact as cosmologically meaningful. Lines indicate openings, flows of Kindness; dots indicate closures, applications of Judgment. The space between them is mediation — Mercy. Every letter is a specific configuration of these three modes.
The consequence is that no letter is just a phonetic sign. Each letter carries a particular calibration of Kindness, Judgment, and Mercy. When letters combine to form a Name (Op. 23) or a word, the combination produces a specific cosmic effect — because the underlying CHaDaR-mix produces that effect at the executive level.
This logic prepares the combinatorial doctrine that becomes important in Op. 22 (the four expansions of the Four-Letter Name) and beyond. The cosmic government's operational arithmetic — counts of sparks, expansions of Names, configurations of letters — is meaningful because each letter is itself a meaningful combination, and the combinations of combinations carry cosmological weight throughout.
Op. 116 will name CHaDaR as Zeir Anpin (Z"A)'s governmental order — Kindness/Judgment/Mercy running through the operational Partzuf from body up through the Mochin. The same three-fold structure Op. 20 plants at the letter level operates at the Partzuf level. Op. 20's combinatorial logic is the cosmic government's executive grammar.