Speak
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.
Jeremiah 11:17-18
17
For Yahweh of Armies, who planted you, has pronounced evil against you, because of the evil of the house of Israel and of the house of Judah, which they have worked for themselves in provoking me to anger by offering incense to Baal.
18
Yahweh gave me knowledge of it, and I knew it: then you showed me their doings.