John 16:31

31.Do you now believe? As the disciples were too highly pleased with themselves, Christ reminds them that, remembering their weakness, they ought rather to confine themselves within their own little capacity. Now, we never are fully aware of what we want, and of our great distance from the fullness of faith, till we come to some serious trial; for then the fact shows how weak our faith was, which we imagined to be full. Christ recalls the attention of the disciples to this matter, and declares that they will ere long forsake him; for persecution is a touchstone to try faith, and when its smallness becomes evident, they who formerly were swelled with pride begin to tremble and to draw back.

The question put by Christ is therefore ironical; as if he had said, “Do you boast as if you were full of faith? But the trial is at hand, which will disclose your emptiness.” In this manner we ought to restrain our foolish confidence, when it indulges itself too freely. But it might be thought, either that the disciples had no faith at all, or that it was extinguished, when they had forsaken Christ, and were scattered in all directions. I reply, though their faith was weakened, and had almost given way, still something was left, from which fresh branches might afterwards shoot forth.