14 Then one of the Twelve, who was called Judas Iscariot, went to the chief priests  15 and said, “What are you willing to give me if I hand him over to you?” They paid him thirty pieces of silver,  16 and from that time on he looked for an opportunity to hand him over. (26:14-16) 

There is only one previous reference to Judas (10:4) – even there we were informed that Judas betrayed Jesus.  In these few verses we discover the nature of that betrayal: (a) it is at Judas’ initiative, and (b) Judas asks for money.  The text gives no reason for the betrayal, but the actions stand in stark contrast to the woman (26:6-13) who has just anointed Jesus’ head – something Jesus identifies as a preparation for burial – which Judas is seemingly arranging.

R.T. France (1989, 267-8) notes that Judas’ actions are a “cold business proposition. The reason for his action can only be guessed. John 12:6 tells us that he had an eye for financial gain, and the sum involved (equal to 120 denarii) was not inconsiderable, but few have been able to believe that this was enough to cause such a radical volte-face. If he was the only Judean in the group he may have resented the leadership of the Galilean fishermen, but even cultural pride would hardly turn him against one whom he still believed in. More likely he was disillusioned that Jesus’ idea of Messiahship (just graphically confirmed in v. 12) was not that for which he had joined the movement; with the threat of imminent official reprisals instead of the triumphant leadership of Israel he may have been hoping for (cf. 19:28), it was time to get out before it was too late. He may even have concluded sincerely (as did Saul of Tarsus) that Jesus was after all a false prophet, who must be destroyed. Whatever the reason, Matthew does not present him as a reluctant informer.”