巠 is the original (
本字) form whose meaning was 'underground watercourse' or, in the loom sense, 'warp threads strung lengthwise on a frame'. The bottom
工-shape was originally a loom or frame; the three vertical strokes on top depict the warp threads passing through. Adding
纟 (silk radical) gave the modern
经 specifically for 'warp / classic / channel'.