“perspicuitas: perspicuity, clarity of thought, lucidity;
one of the traditional attributes of Scripture. The attribution of perspicuitas to Scripture does not imply that all passages are clear; rather, the point is that all thins necessary to salvation are clearly stated.”Richard Muller, Dictionary of Latin and Greek Terms: Drawn Principally From Protestant Scholasticism, Term: perspicuitas.
As for the more difficult portions of Scripture,
“the obscurities in the text are to be elucidated through comparison to and collation with clear passages in accordance with the analogy of Scripture and the analogy of faith.”Muller, Dictionary, Term: perspicuitas
The Christian employs the former [i.e., analogy of Scripture] by comparing less clear Scriptures with the clearer passages of scripture on that topic or theme. The latter [i.e., analogy of faith] is based in Romans 12:6 […the proportion of faith] coupled with an assumed sense of Christian teaching for a given theological idea on the part of the Christian. In sum, Scripture is clear [perspicuous] or becomes clear to the Christian when he/she interprets the difficult parts of Scripture with Scripture itself coupled with Christian study in Christian theology.