speak from

speak from something

to draw authority or credibility in one's speaking from something such as knowledge or experience. Believe me, I speak from experience. Listen to her. she speaks from a lot of knowledge and training.
See also: speak
References in classic literature ?
I knew, too, that this was the first time in the entire history of the Negro that a member of my race had been asked to speak from the same platform with white Southern men and women on any important National occasion.
Today when we say that people speak from their hearts, we mean they speak with feeling or emotion and not just abstractly or from their "heads.