Neither failure nor hostility can weaken the messenger’s conviction that he has been sent by Jesus. That his word may be their strength, their stay and their comfort, Jesus repeats it. “Behold, I send you.” For this is no way they have chosen for themselves, no undertaking of their own. It is, in the strict sense of the word, a mission. With this, the Lord promises his abiding presence, even when they find themselves as sheep among wolves, defenceless, powerless, sore pressed and beset with great danger. Nothing can happen to them without Jesus knowing of it.
Dietrich Bonhoeffer, The Cost of Discipleship, p. 236-237.
(Commenting on Matthew 10:16-25)