In just being honest, for me growing up as a young man, I saw the OT and NT as almost different religions. Ya wrath is a God of battle, vengeance, awe, and war. Jesus seems the antithesis. It’s hard seeing Jesus being ok with wiping out the Amalekites or being cool with 100 dead Philistines slaughtered for David’s foreskin trophy bag to Saul. The pacifism, warmth, comfort, and humility of Jesus seems incongruent with turning Sodom into a Walmart parking lot or the face-melting butt-kicking of the Old Testament.....
But when you listen to Jesus talk about Gehenna, you do a double-take and say, “wooah, wait..., um, what was that, Lord?” The narrow gate talk, gnashing of teeth stuff, mill stone tied around your neck business.....yep, the Old Testament lives!!
Free will, the essential central aspect of love, makes everything messy. The people in the age of Noah weren’t ready for Christ! The age of the Exodus was a time of pagan selfishness. Look at how even Israel gives in to idolatry!! The age of David through Rehoboam to Hezekiah is decadent. I think God needed civilization in the world to bring the faith to us all. The Greeks and Romans gave that to the world. The Greek myths, the Roman laws, the poetry, the search for truth and beauty, the philosophy of Aristotle, Socrates, Plato. The sciences, the idea of civility vs. barbarism....I personally feel that is why God brought His Son to us in Roman times.
But in the Old Testament, God had little choice but to allow blood and war and butt-kicking as a concession to protect Hos People Israel. Until civilization could come and Christ could be in our midst, God had to do what is hard....and sad.