Why can Fillmore's letter be seen as a masterful combination of salesmanship, diplomacy, and firmness

Fillmore's letter was full of diplomacy, commercial ability and firmness, the president always referred to the Japanese authority as "your majesty", this represented the diplomatic recognition of the one who governed Japan at the time, besides that, he also treated him very kindly so that Japan agreed to trade with the United States, and at the same time exhort him firmly to abandon the old policies that restricted them from doing business with foreign countries on the one hand, and open up to new forms of trade, explaining how, when and what they could trade.