Adam Clarke on John 13:27

Satan entered into him - He had entered into him before, and now he enters again, to strengthen him in his purpose of delivering up his Master. But the morsel was not the cause of this entering in; the giving of it only marks the time in which the devil confirmed Judas in his traitorous purpose. Some have thought that this morsel was the sacrament of the Lord's Supper: but this is an utter mistake.

That thou doest, do quickly - As if he had said: "Thou art past all counsel; thou hast filled up the measure of thy iniquity, and hast wholly abandoned thyself to Satan; I will not force thee to turn from thy purpose, and without this thou wilt not. Thy designs are all known to me; what thou art determined to do, and I to permit, do directly; delay not, I am ready."