{But they understood not the saying} (hoi de (8867)nooun to
rh(886d)a). An old word. Chiefly in Paul's Epistles in the N.T.
Imperfect tense. They continued not to understand. They were
agnostics on the subject of the death and resurrection even after
the Transfiguration experience. As they came down from the
mountain they were puzzled again over the Master's allusion to
his resurrection ( Mr 9:10 ).  Mt 17:23  notes that "they were
exceeding sorry" to hear Jesus talk this way again, but Mark adds
that they "were afraid to ask him" (ephobounto auton
eper(9374)(8873)ai). Continued to be afraid (imperfect tense), perhaps
with a bitter memory of the term "Satan" hurled at Peter when he
protested the other time when Jesus spoke of his death ( Mr 8:33  Mt 16:23 ).  Lu 9:45  explains that "it was concealed from them,"
probably partly by their own preconceived ideas and prejudices.