Matthew 27:6
And the chief priests took the silver pieces, and said, It is not lawful for to put them into the treasury, because it is the price of blood. And the chief priests took the silver pieces, and said, It is not lawful for to put them into the treasury, because it is the price of blood.
The thirty pieces of silver paid for the betrayal and death of Jesus were regarded by the chief priests as the price of blood and therefore unlawful to put into the temple treasury. Rather than restore the money to sacred use, the priests used it to buy a potter's field as a burial place for strangers. That burial field became known as the Field of Blood. The use of the money and the naming of the field fulfilled prophecy, identified as Zechariah's prophecy about the thirty pieces of silver being cast to the potter.
Judas's confession in connection with returning the money testified to the innocence of Jesus. The verse belongs to the account of Judas's betrayal and its aftermath. Judas's death in that aftermath is a fearful sign of retribution already coming upon those guilty of the blood of Jesus. The chapter belongs to the history of professedly pious people and warns that religious profession does not excuse conduct contrary to God's law.