It seems that moral and spiritual conditions in the kingdom had so declined (perhaps as a result of war), that,
"there came prophets among the people, who were sent from the Lord, prophesying that the wickedness and idolatry of the people was bringing a curse upon the land, and they should be destroyed if they did not repent. And . . . the people did revile against the prophets, and did mock them. (Ether 7:23-24)
It is not specified here just exactly what the term "idolatry" implies, but Moroni writes that "the Lord did spare them, and they began to prosper again in the land" (Ether 7:26) which is covenant language related to the promised land covenant given to the brother of Jared:
And [the Lord] had sworn in his wrath unto the brother of Jared, that whoso should possess this land of promise, from that time henceforth and forever, should serve him, the true and only God, or they should be swept off when the fulness of his wrath should come upon them. (Ether 2:8)
Thus, apparently the Jaredites were worshiping other gods than the Lord Jehovah. However, unlike some other times in history, King Shule passed judgment on those who abused the prophets and issued a decree allowing the prophets to go wherever they wished, unharmed and unhindered. Once the prophets were protected by law, people listened and were brought to repentance. The apparent result of these actions was that,
there were no more wars in the days of Shule; and he remembered the great things that the Lord had done for his fathers in bringing them across the great deep into the promised land; wherefore he did execute judgment in righteousness all his days. (Ether 7:27)
[Alan C. Miner, Personal Notes]
Geographical [Theory Map]: Ether 8:2 - 8:6 Jared Comes to the Land of Heth (Chronology)