Tell me, please, how do 我's radicals 手 and 戈 create the meaning of 我 (ie: I)? I know that 戈's pictogram (象形) means a rake-like tool or weapon, borrowed for sound to mean "me" (note 'Oracle bone script')." But then how did "rake-like tool or weapon" shift semantically to mean "I"?
我 was a kind of weapon.
According to the book 字源谈趣,
我 was a kind of broadax originally in slavery society.
And then later,
我 was obsoleted by other new weapons little by little. From Han and Tang dynasty,
我 was borrowed to be used as first person, and the pronunciation doesn't change till today.
This phenomenon is called 假借字, means select and use an old word for new expression and meaning, without creating a new word.
Additional reference: 汉字“我”最早是杀人凶器
Phonetic loan. The social hierarchy in Chinese society was such that one had to use pronouns according to class. 朕 (zhèn) means "I", but was eventually used exclusively by the emporor, and nobody was allowed to be equal to him. Therefore a range of honorific pronouns exist in Chinese, many of which are loan words or otherwise obscure.