Being well aware of many similar compilations, past and present (he mentions in his own time ha-Aggadah by Bialik and Rawnitsky, as well as Torah Temima) he differentiates all these from his own by claiming that his purely concerns biblical interpretation, rather than aggadah and mussar. The intention is to present a clear Torah commentary as seen through the words of Chazal. He writes that he can't understand why no one had done this before. He also has a little side attack on Bible critics who emend the text wildly without even having enough sense to use dictionaries or lexicons which presumably if they used they would realize that they are not as competent Bible scholars as they think. Such scholarship is called madda (i.e., scientific) because people don't know better, and then it gets repeated, canonized and raised to the level of Torah from Sinai. Therefore he feels that in his own time it is a double obligation to make such a compilation, to show the true interpretations of the rabbis.
Interestingly, not only is the book dedicated to Leonard Cohen's father Nathan (and two others, one of whom is the author's son) but at the end of the introduction is a mention of Leonard himself, then just a few weeks shy of 5 years old (as well as his mother Masha, and the other members of the family):

I wonder if Leonard Cohen knows of his grandfather's shout-out to him.
As for who the author was, by the description of his grandson (see here) it sounds like he was one of those maskil torani types that time and some people forget or act like they forget existed (the author refers to his "friend" Prof. Louis Ginzberg in the introduction, which was done in those days). Leonard said that he was a student of R. Yitzchak Elchanan, but of course I have no idea what that means. He also says that he "closed his eyes" when R. Yitzchak Elchanan died. I think the authority for that was Masha Cohen, who also said that people came 100 miles to hear him lecture in Kovno. So I guess the point is that he was a talmid of R. Yitzchak Elchanan. Unfortunately I didn't yet uncover even basic facts like year of his birth or death.