Here are the rest of Amy Carmichael’s thoughts on Luke 10:19:

     Sometimes we do not feel in the least like treading down scorpions and serpents and all the power of the enemy.  Perhaps we are allowed to feel our nothingness, so that we may in the depths of our heart understand these other words “Without Me you can do nothing” (John 15.5).  I think there was something of this in our Lord Jesus’ mind, when He told the story of one who had nothing to set before his friend–not a crumb–and it was midnight.  [Cf. Luke 11.5-8] When we do not feel victorious and have nothing to give to others, it is in truth “midnight” in our soul, “the dark night of the soul”, old writers called it.
     But we have  God to Whom we can go at any minute, the weakest minute, the darkest minute, “at midnight”.  “Be Thou my strong habitation, whereunto I may continually resort: Thou hast given commandment to save me; for Thou art my Rock and my Fortress” (Ps 71.3).  And if it be victory over the power of the enemy in our own hearts that we need, He will give us not just crumbs, but loaves–“He will rise and give him as many as he needs” (Luke 11.8).

[For a related link, see “When you feel like you have nothing left to give . . . “]