As for the changes, that was in line with the changes of the understanding that Man had of God, even more so now that he spoke directly though his ONLY BEGOTTEN Son.
Take death for example, from the early books of the NT through the middle one to the NT, you see a gradual "shift" in underdtanding of what death was, the sate of the dead and even what the ressurection meant.
Not all agreed mind you, look at the Saudacees and Pharasiees and their disagreement about death and the ressurection and angles and spirits and they were BOTH Hebrew sects.
The fact that God "changed" from Genesis to the Gospel of John means that their understanding of God changed, they became more enlightended, the message was clear because the messenger was divine, infalliable, unlike those before him.