Midrasch zu Hoschea 5:12

R. Judah the son of Shalum maintained: Moses desired to write down the Oral Law (Mishnah) as well, but the Holy One, blessed be He, foresaw that in the course of time nations would translate the Written Law and read it in the Greek language. They would then assert: “We, too, are Israelites.” Hence the Holy One, blessed be He, told Moses: Should I write for him never so many things of My Law (Hos. 8:12), the result being: They (Israel) are accounted as strangers (ibid.). Why to this extent? Because the Oral Law contains the mysteries of the Holy One, blessed be He, and He reveals His mysteries only to the righteous, as it is said: The counsel of the Lord is with them that fear Him (Ps. 25:14). Similarly you find that after the Sodomites angered the Holy One, blessed be He, and He was moved to destroy them, He consulted only Abraham, as it is said: Shall I hide from Abraham that which I am doing?