Final answer:
The promise to convert good words into good deeds likely refers to the U.S. providing practical aid to South America, supporting their stability and prosperity in a non-imperialistic manner.
Step-by-step explanation:
The message to "our sister republics south of our border" that promises to convert good words into good deeds most likely means the United States will establish programs to give practical aid to the poor of South America. This interpretation aligns with the historical context and excerpts given, suggesting that the United States desired to see neighboring countries become stable, orderly, and prosperous. It emphasizes the United States’ commitment to supporting the welfare and self-government of nations in the Western Hemisphere, as outlined in the Monroe Doctrine and further sentiments expressed by historical figures like Abraham Lincoln regarding the importance of union and reconciliation, and not as an imperialistic or militaristic endeavor.