The Jews were trying to continue the original monotheistic thought that started in Egypt (Aten). Maybe Moses is the link between Aten and YHVH. Maybe he had access to the secret cult of Aten.
YHVH was just one god among many gods. And for some reason they chose YHVH to be the monotheistic God.
The purpose was to stablish monotheism.
YHVH is not the equivalent of the First Person, the Father.
YHVH is the Hebrew equivalent to the Godhead. But to Christians the Godhead is a complete mystery.
Jesus revealed the Trinity. YHVH it's not the Father.
Christianity brought a new concept beyond the Godhead. This is very complex but that's the very reason why St. Stephen was killed. His speech is about this problem of YHVH vs the Father.