Why is the God of the Old Testament so different from the God of the New Testament?
Perhaps broaden your perspective and explore some Eastern ideas. Might help you find the solution to your question.
Study the Egyptian myth of Osiris reincarnation into Horus. If you study the biblical text it is purporting that that myth actually happened in Jesus character being the son a reincarnation of the father.
The LORD Almighty will bless them, saying, "Blessed be Egypt my people, Assyria my handiwork, and Israel my inheritance." Isaiah 19:25
"The lord" of the bible is Egyptian.
John 14:9 Jesus answered: "Don't you know me, Philip, even after I have been among you such a long time? Anyone who has seen me has seen the Father. How can you say, 'Show us the Father'?
Because it was designed to appeal to a different audience.
The Hebrew scriptures dealt with the things that concerned the Hebrews at the time. The Greek scriptures dealt with the things that concerned the empire.