3 Nephi 4

 After the Nephites and Lamanites were preserved from the Gladiaton robbers, -

"...they did rejoice and cry again with one voice, saying: May the God of Abraham, and the God of Isaac, and the God of Jacob, protect this people in righteousness, so long as they shall call on the name of their God for protection.

31 And it came to pass that they did break forth, all as one, in singing, and praising their God for the great thing which he had done for them, in preserving them from falling into the hands of their enemies.

32 Yea, they did cry: Hosanna to the Most High God. And they did cry: Blessed be the name of the Lord God Almighty, the Most High God.

33 And their hearts were swollen with joy, unto the gushing out of many tears, because of the great goodness of God in delivering them out of the hands of their enemies; and they knew it was because of their repentance and their humility that they had been delivered from an everlasting destruction."  (3 Nephi 4:30–33)

Why did they eventually turn from this testimony?