...a type of commitment in which the parents of a boy and agirl agreeon having them marry.
According to the information available on this excerpt, a betrothal is a promise which can be later modified, in which the parents of a boy and a girl promise to marry them. This could also be a definition of arranged marriage.
It is a warning that indicates a future event.
This quote has no mention of a deity (divine authority) or society as a whole (civil obedience), and the only mention of gender is the author's reference to his sibling as "brother." The final line "<span>I won't be caught betraying him." drives the assumption that failing to do his "duty to [his] brother" would violate some sort of bond between he and his brother. Since we only know this relationship as familial, we must assume familial loyalty is the theme.</span>
<span>Debes hacer clic en "Olvidé mi contraseña" y seguir estos pasos.
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Espero que esto ayude!