Helaman 10:13

Now behold, notwithstanding that great miracle which Nephi had done in telling them concerning the death of the Chief Judge, they did harden their hearts, and did not hearken unto the words of the Lord;

Nephi had done an amazing thing. He had told them about the Chief Judge’s death. But they still made their hearts hard. They did not listen to the Lord’s words.

Even after the miracle Nephi had done—revealing the chief judge’s murder—they hardened their hearts and refused to listen to the Lord’s words.