{It was concealed from them} ((886e) parakekalummenon ap'
aut(936e)). Periphrastic past perfect of parakalupt(935c), a common
verb, but only here in the N.T., to cover up, to hide from. This
item only in Luke. {That they should not perceive it} (hina m(880a)aisth(936e)tai auto). Second aorist middle subjunctive of the common
verb aisthanomai used with hina m(885c), negative purpose. This
explanation at least relieves the disciples to some extent of
full responsibility for their ignorance about the death of Jesus
as  Mr 9:32  observes, as does Luke here that they were afraid to
ask him. Plummer says, "They were not allowed to understand the
saying then, in order that they might remember it afterwards, and
see that Jesus had met His sufferings with full knowledge and
free will." Perhaps also, if they had fully understood, they
might have lacked courage to hold on to the end. But it is a hard
problem.