Anyone help me out on that?
[UPDATE: Phil Gons found the quotation, thanks to the suggestion by Pilgrim Mommy. It was after Piper's lecture on John Owen. Piper says:
Now that Phil found the quotation, I remember agreeing with Piper: Alford asks my kind of questions, too.]
When I’m stumped with a . . . grammatical or syntactical or logical flow [question] in Paul, I go to Henry Alford. Henry Alford mostly answers—he . . . comes closer more consistently than any other human commentator to asking my kinds of questions. (John Piper, “John Owen: The Chief Design of My Life—Mortification and Universal Holiness,” 1:30:11–1:30:31).