Has seen translates a Greek perfect tense; heard translates an aorist tense. One the basis of this difference of tenses, some scholars maintain that the emphasis is on “seeing” rather than on “hearing.” However, not all scholars take this position. It is quite likely that no distinction in emphasis should be made here. In 1 John 1.3 both verbs are used in the perfect tense, and the two passages are probably parallel in meaning.

The implication of he tells what he has seen and heard is that “he tells what he has seen and heard in heaven.” Compare 3.11-13.

He tells is literally “he gives witness concerning”; message is literally “witness.” On the meaning of these terms, see 1.7. No one accepts his message may be rendered “no one believes what he has said” or “no one puts confidence in what he has to say.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .