Matthew 10:23
He does not want them to be cowardly — rather the opposite: not, out of longing for the things hoped for, to hand themselves over ready to death and so harm those who are about to be helped by the preaching.
He urges the disciples to flee from this city to another, and from that to another. He says this not teaching them to fear, but not to throw themselves into dangers, die lightly, and harm those who are about to be helped through the preaching (Matthew 10:23).
Greek
Οὐ γὰρ δειλιᾶν αὐτοὺς θέλει, ἀλλὰ τὸ ἐναντίον, μὴ πόθῳ τῶν ἐλπιζομένων ἑτοίμους παραδιδόναι ἑαυτοὺς εἰς θάνατον καὶ ζημιοῦν τοὺς μέλλοντας ἐκ τοῦ κηρύγματος ὠφεληθῆναι. Παρακελεύεται τοῖς μαθηταῖς ἀπὸ τῆσδε φεύγειν τῆς πόλεως εἰς τὴν ἄλλην καὶ ἐξ ἐκείνης εἰς ἑτέραν. τοῦτο δὲ λέγει οὐ δι δάσκων αὐτοὺς δειλιᾶν, ἀλλὰ μὴ ῥίπτειν ἑαυτοὺς εἰς κινδύνους καὶ ἀποθνῄσκειν ῥᾳδίως καὶ ζημιοῦν τοὺς μέλλοντας ὠφεληθῆναι διὰ τοῦ κηρύγματος.