John 12:35

Then Jesus said unto them
Not directly answering to their questions, but suggests to them their ignorance and stupidity, amidst so much light, that was about them:

yet a little while is the light with you:
meaning either himself, the light of the world, ( John 8:12 ) ( 12:46 ) , who was to be but a very little while longer with them, a few days more, and he was to go away from them by death, and be seen and heard no more by them: or the Gospel, which, though that was to continue somewhat longer, it being, after Christ's death, resurrection, and ascension, to be preached to the Jews, both in Judea, and in other parts of the world; yet that would be but for a little while, as the event has shown; for the Jews rejecting the Gospel, and putting it away from them, the apostles, as they were ordered, turned to the Gentiles, ( Acts 13:46 Acts 13:47 ) ;

walk while ye have the light:
that is, as it is explained in ( John 12:36 ) , "believe ye in the light": which the Persic version adds here, and leaves out there: and the sense is, believe in the Messiah, and in his Gospel; embrace him and that, and walk on in him, and worthy of him and of his Gospel, as children of the light:

lest darkness come upon you;
suddenly, at an unawares; either a greater degree of the darkness of ignorance and unbelief; even a judicial blindness and stupidity, which did seize on that people, and continues upon them to this day; or the darkness of afflictions, calamities, and distress, and which have come upon them to the uttermost, to the destruction of their temple, city, and nation; or else a worse darkness, even blackness of darkness, outer darkness in hell, where are weeping, wailing, and gnashing of teeth.

For he that walketh in darkness, knoweth not whither he goeth;
he cannot see his way, nor the stumbling blocks that lie in it, and the dangers he is exposed unto; nor does he know where it leads, and what is the end of it; and just so it is with a man in a state of unregeneracy, and more especially under judicial blindness: he is not aware of the pits and snares that lie in his way, or of the dark mountains on which he stumbles; and though destruction and misery are in his ways, he knows not that he is going thereunto.