During his long imprisonment, Fray Luis found his understanding of the language of Scripture both tested and deepened. His election to the Bible Chair at Salamanca in 1579, itself marked by further controversy, enabled him to concentrate on the subject dearest to him with the official blessing of his University and with the kind of personal authority which belongs uniquely to those who have suffered for their beliefs and received public recognition of their integrity. The result was a series of Biblical commentaries which are central to his work and which established him as the leading Spanish exegete of his age. It was as an interpreter of the language of the Bible that Fray Luis was to do some of his most creative writing.

Over many centuries of Biblical exposition, it had become customary to discern four ‘senses’ or levels of meaning in Scripture. A piece of doggerel still often quoted in the sixteenth century defined them:

To expound Scripture, therefore, involved more than explaining the surface meaning of the text; it meant probing beneath it, for more hidden levels of significance. This was already evident from the New Testament, which itself resorted to allegory (Gal. iv.22–6), and which consistently interpreted Old Testament texts as finding their fulfilment in Jesus Christ the Messiah.