John Calvin Commentary Matthew 26:3

"Then were gathered together the chief priests, and the elders of the people, unto the court of the high priest, who was called Caiaphas;" — Matthew 26:3 (ASV)

Then were assembled the chief priests. Matthew does not mean that they assembled during the two days, but he introduces this narrative to show that Christ was not led by any opinion of man to fix the day of his death. For by what conjectures could he have been led to it, since his enemies themselves had resolved to delay for a time? The meaning therefore is that by the spirit of prophecy he spoke of his own death, which no one could have suspected to be so near at hand.

John explains the reason why the scribes and priests held this meeting: it was because, from day to day, the people flocked to Christ in greater multitudes (John 11:48). And at that time it was decided, at the instigation of Caiaphas, that he should be put to death, because they could not succeed against him in any other way.