We know it prevailed before the flight from Egypt.

I have heard Hillel say Abraham caused the record to be first opened with his own name, and the names of his sons, moved by the promises of the Lord which separated him and them from all other races, and made them the highest and noblest, the very chosen of the earth.

The covenant with Jacob was of like effect.

'In thy seed shall all the nations of the earth be blessed'-- so said the angel to Abraham in the place Jehovah-jireh.

'And the land whereon thou liest, to thee will I give it, and to thy seed'-- so the Lord himself said to Jacob asleep at Bethel on the way to Haran.