Ether 9:15-35 shows a pattern repeated many times in the Book of Mormon:
1. During the righteous reigns of Emer and Coriantum the people prospered exceedingly (see vv. 15-25)
2. Under the reign of Heth, the people began to join together in secret combinations, and they turned to wickedness (see vv. 26-27)
3. The Lord sent prophets to warn the people of their terrible circumstances (see v. 28).
4. The people of Heth rejected the prophets (see v. 29)
5. The judgments of God fell upon the people (see vv. 30-33).
6. The people humbled themselves and repented and the Lord blessed them again with prosperity (see vv. 34-35).
While the fall from prosperity to wickedness is lamentable, what is also worthy of note here is that the Jaredites were able to be wealthy and remain righteous for more than 225 years (see vv. 15-25). [CES, Book of Mormon Student Manual, Religion 121 and 122, 1989, p. 140]