Why is this word so effective in conveying edwards's purpose to his audience ?

The use of the word was so effective to Edwards because the people he spoke to were people of faith and religion.

Explanation:

To understand this answer we need to analyze the context. First of all, he was one of the most prominent speakers of the era, if not the most. He used the word to communicate with them that God was not a kind forgiving god. Instead, he showed them that if they didn't behave according to his teachings they were all going to go to hell. But the most important factor here is that all of them were people of faith and religion.