Why did the struggle against heresies become an important task of the church in the 12-14 centuries?

The Catholic Church itself is guilty of the appearance of heretics in society. The life of clergymen was too different from the canons of faith. To enrich themselves, the highest dignitaries of the church did not disdain any methods. Intimidation, oppression of their parishioners, the sale of indulgences aroused the anger of progressive people. The growth of cities contributed to an increase in heretics. The state and monarchs were subject to the Church. The appearance of heretics was a serious danger to the Roman Holy See. In the struggle against heresy, the Inquisition was established. A punitive body that persecuted and tried heretics.