I notice that you’re not a Christian. On the surface OT and NT principles appear quite different, but I don’t think many Christians who have studied the issue (perhaps excluding some dispensationalists—I’m not really sure what they believe) would accept that distinction.
The heresy that the God of the Old Testament is not the God of the New Testament is called Marcionism, and is the primary reason the Church went to the trouble of establishing the canon of both Testaments.
Outsiders are of course free to disagree, but orthodox Christianity holds that the core principles of the two Testaments are identical, differentiated only by the difference in circumstance of time.