Why does God seem harsher in the Old Testament?

I hope I don't offend anybody, but I am just getting into reading my Bible to try to better myself and grow closer to God. However, some verses in the Old testament seem very harsh. For example, Deuteronomy 25:11-12 "If two men are fighting and the wife of one of them comes to rescue her husband from his assailant, and she reaches out and seizes him by his private parts, you shall cut off her hand. Show her no pity."