Full Idea
A proof of soundess or completeness is a test, not so much of the logical theory to which it applies, but of the theory of meaning which underlies the semantics.
Gist of Idea
Soundness and completeness proofs test the theory of meaning, rather than the logic theory
Source
Michael Dummett (The Justification of Deduction [1973], p.310)
Book Reference
Dummett,Michael: 'Truth and Other Enigmas' [Duckworth 1978], p.310
A Reaction
These two types of proof concern how the syntax and the semantics match up, so this claim sounds plausible, though I tend to think of them as more like roadworthiness tests for logic, checking how well they function.