This verse must be read as a parallel to the previous verse's lament of the places Judah will turn for supernatural assistance. The last verse ends with the admonition that they should turn to their God. In this verse, that idea is continued. They also turn to the scriptures (law and testimony) to find the word of God. Isaiah notes not only that this is a place for the finding of truth, but that sadly there are those who will read those sources and not find the truth therein. These are they who "have not light in them." They read, but without the communication of the true spirit of God, they read into even the scriptures the things they want to hear, just as they do with the soothsayers.