The reason of revelation:

It is narrated by Ikrimah, that when the Prophet (saws) sent Abu Bakr (may Allah be pleased with him) to Finhas, the Jew, to seek help he (saws) wrote to him and said to Abu Bakr:

“Do not issue a ruling for me until you return to me.”

When Finhas read the book, he said: May your Lord need money now? Abu Bakr said: “I would arm him with the sword, then I remembered the saying of the Prophet (saws). Then this verse was revealed: {Allah has certainly heard the statement of those [Jews] who said, “Indeed, Allah is poor, while we are rich}

سَنَكْتُبُ مَا قَالُواْ وَقَتْلَهُم الأَنبِيَاء بِغَيْرِ حَقٍّ وَنَقُولُ ذُوقُواْ عَذَابَ الْحَرِيقِ { We will record what they said and their killing of the prophets without right and will say, “Taste the punishment of the Burning Fire.}: This is a response that gives good tidings to the Prophet (saws) and strengthens the believers, it is a threat to which the souls of man tremble.

This speech is directed to the Jews who were in Medina, who conspired, who deceived, and who tried to make people suspected the message of the Prophet Muhammad (saws) and the Holy Qur’an.