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.
Matthew 8:18-20
18
Now when Jesus saw great multitudes around him, he gave the order to depart to the other side.
19
A scribe came, and said to him, "Teacher, I will follow you wherever you go."
20
Jesus said to him, "The foxes have holes, and the birds of the sky have nests, but the Son of Man has nowhere to lay his head."