what is the reason behind the ruling of not mixing meat with milk for the jews ??

Answer 1

This is discussed in the Talmud, Masechta Chullin on pages 113b and 115b. It boils down to the fact that the terms used are generic ones and can be understood to refer to any animal within milk- not to an animal specifically being cooked in the milk of its mother. An example of a generic term in the statement "You shall not cook a kid in its mother's milk" is the word "gdi"- translated as kid but seen as a reference to any young animal (such as calf or lamb) unless it is specified to be of a specific species.

The idea that meat represents death (the slaughter of the animal), while milk represents new life, and it is not proper to mix life and death is from a few different sources Reecanti; Tzeror HaMor; Zohar 2:124b. The idea of it being forbiddenas meat cooked in milk was an idolatrous practice, especially on festivals is brought by the Rambam in Moreh Nevukhim 3:48 and by the Ralbag

Answer 2

The Torah states, "Do not cook a kid [goat] in its' mother's milk" (Exodus 23:19)
Cooking and/or eating meat and milk together was an idolatrous practice, and idolatrous practices are forbidden by the Torah.
Also, according to Kabbalah, milk symbolizes life and meat symbolizes death, and combining the two creates a spiritual clash.
For a lot of Jewish people nowadays it just means you can't have milkshake with your burger and fries.

Answer 3

Probably to avoid cross-contamination and infections such as T.B.

Most of the laws are excellent in a pre-refrigeration society.

Answer 4

it's really to do with food hygiene as a lot of these practices were put in place before refrigeration was round.