'Word,' as in Isaiah 9:8, signifies the doctrine of internal and external worship. 'Word,' as in Psalms 119:6-17, stands for doctrine in general.

'The Word,' as in Psalms 147:18, signifies divine good united with divine truth.

The whole Word is nothing but the doctrine of love towards the Lord, and love towards our neighbor, as in Matthew 22.

(References: Arcana Coelestia 1288)

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.