Here bayān may also mean furnishing an argument. A proposition can be linguistically clear while its truth remains disputed; in that case the needed explanation is evidential rather than lexical.
Someone may understand the words “the world exists” yet demand a justification for affirming objective reality.
Three stages should be distinguished: recognizing the words' meanings, understanding what is asserted, and judging the grounds for the assertion sufficient. Different debates require different forms of clarification.