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.
Romans 15:19-21
19
in the power of signs and wonders, in the power of God's Spirit; so that from Jerusalem, and around as far as to Illyricum, I have fully preached the Good News of Christ;
20
yes, making it my aim to preach the Good News, not where Christ was already named, that I might not build on another's foundation.
21
But, as it is written, "They will see, to whom no news of him came. They who haven't heard will understand."