Why did God change character noticeably between the Old and New Testament? It's as if he'd been through therapy or something in the meantime. Seems like he really lightened up a lot. Dealt with some of his anger issues and possessiveness.
Or did it represent the product of a different culture/era?
There are several possibilities:
1) the first is culture - the ancient Israelites were quite a stubborn people and frequently getting into trouble. Moses goes away a short period and they go right back to worshipping a golden calf. The laws of Moses were directed to a stubborn group of people with a different culture and era.
2) There are degrees of laws - in other words, there are orders of laws. Moses actually came down from the mountain twice. The first set of tablets he dropped and broke. It is suspected, if the Israelites weren't causing mischief they would have had laws similar to when Christ came. Moses returns to God for more tablets and God says, "fine, here are the harder rules." When Christ comes, he brings the "higher law" with the two great commandments - love God and love your neighbor.
3) God is a God of justice and mercy. Justice in the sense that he sets a rule and consequence and can't vary from it. Otherwise, God would be a liar. The old testament is all about God's justice and gives the people a reason to look forward to Jesus Christ with the introduction of mercy. It's no longer and "eye for an eye and tooth for tooth." Problem is the Israelites completely missed who Jesus Christ was and put him to the cross
I'm not sure why we hold onto the Law of Moses. Jesus Christ fulfilled the law - setup a "higher" set of rules and told us to follow those. Matt 5:17-22. Obviously, for some Christians, results may vary.