What did Yahweh tell Moses the song would do when many evils and troubles found the people of Israel?

Yahweh told Moses that the song would testify before Israel as a witness and it would not be forgotten out of the mouths of their descendants.

What did Yahweh say he knew about the people even before he brought them into the land that he had sworn?

Yahweh said that he knew the plans that the people were forming today.