Mateo 10:19

Be not anxious

(μη μεριμνησητε). Ingressive aorist subjunctive in prohibition. "Do not become anxious" (Mateo 6:31). "Self-defence before Jewish kings and heathen governors would be a terrible ordeal for humble Galileans. The injunction applied to cases when preparation of a speech would be impossible" (McNeile). "It might well alarm the bravest of these simple fishermen to be told that they would have to answer for their doings on Christ's behalf before Jewish councils and heathen courts" (Plummer).

Christ is not talking about preparation of sermons. " In that hour " (εν εκεινη τη ωρα), if not before. The Spirit of your Father will speak to you and through you (Mateo 10:20). Here is no posing as martyr or courting a martyr's crown, but real heroism with full loyalty to Christ.