《三摩地王经》说：
『若毁此瞻部洲中一切塔，若毁谤契经，此罪极尤重。若杀尽殑伽沙数阿罗汉，若毁谤契经，此罪极尤重。』

如果能对前三种殊胜获得定解，就会感到佛语中无一字可舍，完全视为实修教授，生起平常的恭敬心。如此一来，就不会分判法的优劣，自然遮挡最严重的谤法之门。

节录来自《掌中解脱》

补充资料：
前三种=课判---甲二----令于教授起敬重故开示其法殊胜---
乙一、通达一切圣教无违殊胜
乙二、一切圣言现为教授殊胜
乙三、易于获得胜者密意殊胜

The faults of those who slander the dharma are extremely grave.

In The King of Concentrations Sutra, it states that the sins of slandering and abandoning the sutras, and teachings, are extremely weighty. As it is equivalent to one having destroyed all stupas in Jambudvipa, and killing arhats that are as many as grains of sand in the Ganges River. 

If we are able to arise the 3 greatness*, we will realize that not a word by the Buddha can be abandoned. It is to be fully viewed as the instructions for true practice, and to generate a respectful attitude. In this way, we will not differentiate if the teachings are good or bad. We will naturally prevent serious defamation of the dharma.  

Translated from the excerpts from Liberation in the Palm of Your Hand

*3 greatness - Outline of text for Lamrim Chap 2 The Greatness of the Teaching: 
II. Showing the greatness of the teaching in order to engender respect for the instructions
A. The greatness of enabling one to know that all of the teachings are free of contradiction (pg 46)
B. The greatness of enabling one to understand that all of the scriptures are instructions for practice (pg 50)
C.  The greatness of enabling one easily to find the Conqueror's intent (pg 53)