Why did Patriarch Nikon's reforms lead to the Old Believers movement?

Patriarch Nikon’s reforms, initiated between 1652 and 1667, aimed to align the Russian Orthodox Church with contemporary Greek Orthodox practices. Over centuries, Russian liturgical books and rituals had diverged from their Greek origins due to transcription errors and local adaptations. Nikon sought to "purify" these by mandating changes such as using three fingers instead of two when crossing oneself, altering bowing forms, and revising liturgical texts to match Greek models.123

These reforms triggered the Raskol (Great Schism) because many clergy and laity viewed the changes as a betrayal of holy traditions essential for salvation. Traditionalists, led by figures like Avvakum Petrovich, denounced the reforms as the work of the Antichrist.21

Despite Nikon’s eventual deposition, the church councils of 1666–67 upheld his reforms and anathematized those who resisted. These dissenters, known as Old Believers, faced persecution for their refusal to abandon ancestral rites, eventually splitting into various priestly and priestless sects that persisted for centuries.231