From
The Macartney Embassy to China, 1792-94, by Paul Gillingham.
The cultural differences between East and West were especially marked when it came to the kowtow. To the Chinese, the act of self-abasement in the form of kneeling three times and ‘knocking’ the head on the floor nine times was a vital element in court ritual. Its significance went far deeper than merely showing respect, as a deep bow or curtsey might indicate in the West. The kowtow was an acknowledgement of the rights and obligations owed to a higher by a lower power.
In Chinese eyes the emperor was the intermediary between heaven and earth, a lynchpin in the preservation of universal order against the forces of chaos, both human and divine. He was, after all, the ‘Son of Heaven’ and brooked no human equal.
But for Macartney, dropping down on both knees was reserved for begging for mercy, praying to God and proposing marriage. To kowtow to the Emperor of China was an act of abject humiliation which he, as the emissary of an equally proud nation, was simply not prepared to do.
The emperor’s mandarins did all they could to persuade the English to change their minds. Zhengrui, Wang and Qiao, who escorted the embassy to Peking, offered to give lessons in kowtowing. They advised the English to replace their tight court breeches, knee buckles and garters in favour of the loose Chinese-style garments that made kowtowing so much easier.
But Macartney remained adamant. How could he make an obeisance before the emperor which he would never perform before his own king? The only terms under which he might agree were if the emperor’s emissaries agreed to kowtow before the portrait of King George, which, for the Chinese, was impossible. The furthest he would go was to drop on one knee and kiss the emperor’s hand, which was how he greeted his own sovereign. Eventually, the Chinese agreed that Macartney could do as he would at home, though they drew the line at hand-kissing. The concession was granted on the grounds that these were, after all, distant barbarians who could not be expected to understand the real significance of the kowtow anyway.
This barbarian doesn't want to kowtow, but will drop to one knee. That's as far as I'll go.