Just ran across this in the (often neglected) back pages of Cranfield’s good commentary on Mark (Cambridge Greek Testament Comm., 1977 ed.):
Mark … tried to state the facts of what he believed to be God’s self-revelation as accurately as he could, refraining from all attempts at improving on them by artistry, precisely because he was a serious theologian—too good a theologian not to recognize the folloy of trying to … varnish sunlight (479).
Much of value has been contributed [i.e., in the last decade or so on 'the theology of Mark']. But the student who is about to engage in an exploration of this literature will be well advised to make sure that his equipment includes a considerable supply of grana salis (480–81).
(Even without Latin fluency grana salis should be obvious! And if not, Google can resolve your perplexity.)