In his post, The perspicuity of Scripture, Ben Myers quotes from Berkouwer's "fine book", Holy Scripture (Grand Rapids, Eerdmans, 1975), p. 275.
He begins his post, "Reformation theologians spoke of the "clarity" or "perspicuity of Scripture ... According to Reformation theology, the message of salvation shines out clearly from Scripture through the power of the Holy Spirit."
He emphasizes that "the confession of perspicuity meant that through the witness of the Spirit the message of the gospel becomes clear and compelling here and now as the Bible is read and (especially) preached."
He, then, quotes Berkouwer, " ... According to the Reformers, the force behind this connection of message and words was the power of the Spirit ... "