In Luke 12:51, 53: By father against son, and by son against the father, is understood evil against truth, and truth against evil; and by mother against daughter, and by the daughter against the mother, is understood the lust of falsity against the affection of truth, and vice versa. (Apocalypse Explained 504[31])

(Odkazy: Apocalypse Explained 504)

Like "say," the word "speak" refers to thoughts and feelings moving from our more internal spiritual levels to our more external ones -- and ultimately from the Lord, who is in a sense the most internal spiritual level of all. This is generally called "influx" and "perception" in the Writings, meaning they are thoughts and feelings that flow in in a complete way from the Lord, rather than being things we have to think about and figure out. On a number of occasions "speak" and "say" are used together; in these cases "speak" refers more to intellectual instruction in matters of thought and "say" refers more to feelings and affections that flow in directly.