The Scripture (tēn graphēn). Probably Psa 16:10. Jesus had repeatedly foretold his resurrection, but that was all forgotten in the great sorrow on their hearts. Only the chief priests and Pharisees recalled the words of Jesus (Mat 27:62.).
Must (dei). For this use of dei concerning Christ’s death and resurrection see Mar 8:31; Mat 26:54; Luk 9:22; Luk 17:25; Luk 22:37; Luk 24:7, Luk 24:26, Luk 24:44; Joh 3:14; Joh 12:34; Act 1:16. Jesus had put emphasis on both the fact and the necessity of his resurrection which the disciples slowly perceived.