It`s written in ancient Chinese.We can paraphraze it into modern Chinese"您为什么不肯养育五月出生的孩子“，which means"Why are you reluctant to bring up the child who was born in May.More details in 孟尝君列传.

君所以不举五月子者，何故 "My Lord, 'tis you want not in rearing those born in the month of May, for what reason?" Here's some clarification... This is a dialogue between a minister and his Lord, hence does not mean using the 3rd person form of a respected "you". Ancient Chinese believed those born on the Lunar 5 May are not lucky for the parents, a boy will bring misfortune to the father and a daughter to the mother.

In ancient Chinese notion, '五月子', which means the child who was born on May 5th on lunar calendar, is hard to bring up and harmful to parents. People's attitudes towards such children resembles the one of Oedipus' father towards his son.

君You 所以不(not )举bring up 五月子a kid who was born on May 5 in lunar calendar者，何故(why)?

：D