I hate the very premise of the "God of the OT vs the God of the NT" question- you know, the one that sets up within the question itself an unresolveable dichotomy between a God of violence (the OT) and a God of love and compassion (the NT).
Here’s a thought to start with. I think its very clear Jesus affirmed the divine inspiration of the Old Testament. Out of fidelity to Jesus, I feel compelled to accept this collection of ancient writings as divinely inspired. Yet, also out of fidelity to Jesus, I feel compelled to emphatically repudiate its violence.
What’s interesting is that Jesus himself repudiated the violence of the Old Testament — despite his belief that this collection of writings was inspired. Jesus taught, “You have heard that it was said, ‘Eye for eye, and tooth for tooth.’ But I tell you, do not resist an evil person. If anyone slaps you on the right cheek, turn to them the other cheek also (Mt 5:38-39).
It’s true, as many scholars have argued, that most of the contrasts between what people had heard and what Jesus taught (”you’ve heard it said… but I say“) do not repudiate Old Testament itself but Jewish interpretations that rose up around Old Testament teachings. But this is clearly not the case with this passage, for the “eye for an eye” commanded is explicitly and repeatedly given in the Old Testament (e.g. Ex 21:24; Lev 24:19-20). In fact, this quid pro quo philosophy lies at the very heart of the law, especially its required violent punishments.
Most interestingly, in Deuteronomy Moses goes so far as to stress that the law must not be waved aside out of compassion. “Show no pity,” the text says, “ life for life, eye for eye, tooth for tooth, hand for hand, foot for foot” (Deut 19:21). Yet, Jesus not only commands people to “show pity,” he replaces the Old Testament quid pro quo ethic with his radical ethic of unconditional love.
For example, while the Old Testament allowed Israelites to hate their enemies and sometimes command them to slaughter them, Jesus forbid his disciples from ever hating or doing any harm to an enemy. Instead, he commanded people to “love your enemies and pray for those who persecute you” (Mt 5:43-45). Luke includes the command to “do good to those who hate you, bless those who curse you” and “pray for those who mistreat you” (Lk 6:27-28).
...I’ll leave you with this teaser thought: Is it possible that some divinely inspired material is not supposed to reveal to us what God is like but what he is not like? Is it possible that some material is inspired precisely because God wants us to follow Jesus’ example and repudiate it?
Abraham believed God told him to sacrifice his child, yet he trusted that God was not really like the bloodthirsty Canaanite god Molech and thus would not make him follow through with his request, even though he had no choice but to move forward in obedience. He trusted that God would supply the commanded sacrifice, if only at the last minute (Gen. 22:8).