There must be a reason for the evolution of such an elaborate ceremony, which only says: “I promise.”
It is likely that having gone through such complicated maneuvers, one cannot forget that he made a certain commitment.
It is probably similar to the proverbial making a knot in a handkerchief, which some older readers might remember (It became extinct in the end of the 20th century, with the invention of paper towels and mobile phones.)
There’s evidence that already in ancient Greece, it was agreed that “it is the oath which holds democracy together” (Lycurgus of Athens, 390 – 324 BC.)
Another take on Gulliver taking a Lilliputian oath.
Artist: Jean Ignace Isidore Gérard Grandville (pseudonym of J. J. Grandville), 1835
Indeed, only when people make agreements and keep them, can people survive as a group, with individuals depending on each other and helping each other.
This common knowledge exists from time immemorial, with the Biblical first recorded oath, which God gave humankind, of never again “smiting every living thing.”
With some minor exceptions, He did keep his oath and never produced a colossal, global Flood again.
Mankind has imitated God, but resorted to elaborate ceremonies to impress and imprint the agreements that were made: In ancient Judaism, one held the testicles of the person to whom he gave oath, while pledging to do something. This historical fact is also to be assessed in the Latin testiculus, diminutive of testis, meaning "witness"; the Romans worshiped a stone, curiously naming it ‘Iuppiter Lapis,’ on which pigs were slaughtered and the oath taker begging: 'Strike the Roman people as I strike this pig here to-day, and strike them the more, as thou art greater and stronger.'
(I find it strange that the Roman people never questioned why they were the ones to suffer the consequences of the oath-taker breaking his own oath.)
Then came Jesus, the anarchist, who expressed his displeasure with the authorities of his time by calling on his fellow-man not to be part of their system, not to feel obliged to the oaths, which authorities expected people to respect and abide by. Jesus’ protest was soon embraced by newly emerging authorities, to be used and abused. To confuse people words were joggled: “oath” was replaced with “affirmation” and later with “affidavit.”
Secular and religious authorities of all shades and creeds, who have always recognised the validity of Lycurgus of Athens “it is the oath which holds democracy together,” replaced as they pleased ‘Democracy’ with ‘Republic,’ ‘Communism,’ ‘Fascism,’ ‘Nationalism,’ etc.. Adding the symbolic Holding of the Testicles (in the form of Taxes, Enemies, etc.,) sprinkled the dish with the required amount of Fear, to make it easier for people to swallow, till this day.