John Lightfoot on John 13:27

[And after the sop, &c.] Satan knew well enough what Christ meant by it: for when he saw that by giving the sop Christ had declared which of them should betray him, the devil makes his entry. For as he had entered into the serpent that deceived the first Adam, so he knew the second Adam could not be betrayed but by one into whom he should first enter.

[That thou doest, do quickly.] I would take this expression for a tacit severe threatening pronounced, not without some scorn and indignation against him: q.d. "I know well enough what thou art contriving against me; what thou doest, therefore, do quickly: else thy own death may prevent thee, for thou hast but a very short time to live, thy own end draws on apace." So Psalm 109:8, "Let his days be few." And, indeed, within two days and three nights after this, Judas died.