All the revision in the world will not save a bad first draft: for the architecture of the thing comes, or fails to come, in the first conception, and revision only affects the detail and ornament, alas!

Lawrence is stressing that revision has limits: if the initial conception of a work is structurally unsound—its governing idea, plan, or “architecture” is missing—later polishing cannot supply what was never built into the first draft. In his metaphor, revision can refine “detail and ornament,” but it cannot reliably redesign the load-bearing framework without essentially starting over. The remark reflects a craftsman’s view of writing as construction: the decisive moment is the first shaping of the whole, when purpose, proportion, and narrative or argumentative structure are set. It also cautions writers against overvaluing tinkering and underinvesting in clear initial design.