because He was teaching His disciples. He told them, “The Son of Man will be delivered into the hands of men. They will kill Him, and after three days He will rise.”
Textus Receptus (TR) - Mark 9:31 >Ἐδίδασκε γὰρ τοὺς μαθητὰς αὐτοῦ, καὶ ἔλεγεν αὐτοῖς ὅτι Ὁ υἱὸς τοῦ ἀνθρώπου παραδίδοται εἰς χεῖρας ἀνθρώπων, καὶ ἀποκτενοῦσιν αὐτόν· καὶ ἀποκτανθείς, τῇ τρίτῃ ἡμέρᾳ ἀναστήσεται.