Speaking of "your sister" was an appeal to identity. Speaking about killing a woman raises questions about fame and welfare, and arousing fear of the sinful act of killing one's sister during her marriage ceremony is an aspect of bheda
SB Canto 10.1 to 10.13
In the Viśva-kośa dictionary, the word garbha is explained: garbho bhrūṇe arbhake kukṣāv ity ādi. When Kaṁsa was about to kill Devakī, Vasudeva wanted to dissuade him by the diplomacy of sāma and bheda. Sāma means "pacifying." Vasudeva wanted to pacify Kaṁsa by indicating relations, gain, welfare, identity and glorification. Reference to these five concerns constitutes sāma, and Vasudeva's presentation of fear in two situations-in this life and the next-is called bheda. Thus Vasudeva used both sāma and bheda to pacify Kaṁsa. Praising Kaṁsa's qualifications was glorification, and praising him as a descendant of the bhoja-vaṁśa appealed to sambandha, relationship. Speaking of "your sister" was an appeal to identity. Speaking about killing a woman raises questions about fame and welfare, and arousing fear of the sinful act of killing one's sister during her marriage ceremony is an aspect of bheda. The Bhoja dynasty refers to those who were simply interested in sense gratification and were therefore not very aristocratic. Another meaning of bhoja is "fighting." These were indications of defamation for Kaṁsa. When Vasudeva addressed Kaṁsa as dīna-vatsala, this was excessive praise. Kaṁsa would accept calves as a form of revenue from his poor constituents, and therefore he was called dīna-vatsala. Vasudeva knew very well that he could not by force rescue Devakī from the imminent danger. Devakī was actually the daughter of Kaṁsa's uncle, and therefore she is described as suhṛt, meaning "relative." It is stated that Kaṁsa refrained from killing his close relation Devakī because if he had killed her, a great fight would have ensued among the other members of the family. Kaṁsa refrained from provoking this great danger of a family fight, for it would have caused many persons to lose their lives.