This is an excerpt taken form Got questions: Many who accuse God of being a moral monster mention the wars described in the Old Testament. Or they point to the use of capital punishment for certain acts under the Mosaic Law. The simplest response to these arguments has the advantage of logical strength, although it means little to the average unbeliever. Simply put, if God exists and created life, then He has the authority to decide what happens to that life. He can set the rules, and He can determine the punishments for breaking those rules. If the entire universe is His creation, then “morality,” including life and death, is by definition under His control. Another response to the charge that events in the Old Testament are morally reprehensible is to place all of those events in their historical and scriptural context. When God commanded war against the Canaanites, for instance, it was not some random act of genocide. This was a culture that had been warned about their pervasive evil for centuries, and the time for God to punish that evil had finally come (see Genesis 15:16). When God commanded the death penalty in Israel for certain offenses, it was not in the context of a stable, free, modern environment. It was during a time of great danger, instability, and uncertainty. This same principle applies even in modern societies: we punish crimes in proportion to their damage to the culture. In that day and time, what today would be considered “minor crimes,” if crimes at all, were profoundly damaging to the survival of the culture. Again, the context of God’s commands is important. If God’s plan was to bring the Messiah, the one and only hope of mankind, through Israel, then it’s reasonable that He would take serious measures to protect the survival of that nation. It’s important to realize how deep this topic can be, since a single article could never really do the subject justice. But If you wish to know more on this topic read Paul copan's Book; Is God a Moral Monster? Making Sense of the Old Testament God. If you want the pdf let me know.