The form of the verb spoke in Malachi 3:16 can be understood in one of two ways: as a transitive verb (taking an object; e.g., “He enjoys reading novels”), or as an intransitive verb (not taking an object; e.g., He loves reading).

If the verb is translated transitively, then the object would be the words that the fearers of the Lord spoke to one another, which would follow in the form of direct or indirect speech. This, then, would be the translation: Then those who feared the Lord said to one another: 'The Lord paid attention and heard (what was said by the arrogant evildoers).'

In this case, the words of the fearers of the Lord are in direct opposition to the words of the ungodly who claimed that the Lord evidently does not see or hear what the wicked say or do, because he does not respond! Those who feared the Lord knew that the Lord does hear, with the implication that the Lord will respond when the time is right.

However, if the verb is translated intransitively, then the translation would be as given in the ESV: Then those who feared the Lord spoke to one another, and the Lord gave attention and heard [the words spoken by the faithful who feared the Lord]. In this case, we are not told what they said to one another, but we know that the topic of discussion was what the arrogant evildoers were saying about the Lord.

Grammar itself will not decide how to translate this sentence. In either case, we see in this verse that there remained a faithful remnant who did not agree with what the arrogant evildoers were saying. And from what follows, we may deduce that the Lord was pleased with the discussions of those who feared him.