To comprehend a text, a person must:

1. Become aware of it
2. Have some reason for reading it
3. Find those reasons to be sufficient to spend time reading it
4. Read it
5. Put forth the cognitive effort to understand it (reading something and putting forth cognitive resources to understand it are not the same thing)
6. Succeed in understanding it

Intelligence is just one component of knowledge acquisition, and probably less important than affective issue. Often, intelligence acts indirectly by affecting affect, but in such cases, those effects can be counteracted. The mistaking of performance of cognitive tasks for intelligence is, I believe, often an aspect of the fundamental attribution error.