Answer:
The Hebrews believed in the one true God because of what they had witnessed.
Explanation:
God parted the Red Sea so that they could walk RIGHT THROUGH IT. To this day chariots and bones are found at the bottom of the Red Sea.
They put LAMBS BLOOD on their door posts and no firstborns were killed in their houses. They witnessed the wonderful mighty Power of God and they saw the miracles of His Son, The Messiah. Why shouldn't they believe in the one true God after all they had witnessed?