In "Biblical Perspective" Larry Grile writes:
Luke recorded various times when Jesus had told His disciples of His impending death and resurrection. The quotation of the angel is found in Luke 9:22 and in Luke 18:31-33. Jesus' words, however, had fallen on deaf ears, and the disciples, even including the women of this account, had not comprehended what Jesus was telling them (Luke 18:34).
Source: Building Christian Relationships: Adult Teacher's Insights, page 42.