Even though much of the biblical tradition relates to legends and events that occurred before the giving of the Torah, this total Revelation at Mount Sinai stands at the center of the world of Jewish consciousness.
All the other sources that presumably preceded it, like certain stories of the creation of the world, the origins of the laws and customs of ancient society, and so on, did not reach Judaism independently.
They passed through the great filtering of Divine Revelation at Sinai.
The influences of the outer world, ancient legends and lore of the nations round about, certainly spread to the Jewish people of the time, but it was all cast into the melting pot of the Jewish tradition itself.
The bright light of revelation of the Torah at Sinai fused it into a single entity.
It was a process that was repeated in subsequent generations.
To the extent that external influences did find their way into Judaism, they almost always appeared as subsidiary, not intrinsic to the core.
And indeed there was a certain opposition to them; if they could not be merged, they were ultimately ejected.
When they did melt into the Jewish tradition, they were so thoroughly integrated that it would be almost impossible to identify them as foreign.
–Rabbi Adin Steinsaltz
From a conversation with Rabbi Adin Steinsaltz in Pababola, reprinted in The Strife of the Spirit