This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 曺 is uncertain. It appears to be a variant or older form of 曹, but the precise origin is unclear.
Since the meaning is unclear, focus on the shape: the top looks like a cross 十 over a box, and the bottom is 曰. Think of it as a mysterious container with a label.
For ソウ, imagine a soul (ソウ) trapped inside the boxy shape of 曺, waiting to be released. The soul sound cues ソウ.