How to Know God Exists, considers the claim that the Mosaic Law contains many elements that don't quite match our notions of the sort of law that a perfectly just and perfectly loving God would ordain. There are, e.g. laws that permit the execution of rebellious children, or command the death penalty for homosexuals, idolators, adulterers, etc. There's the casual acceptance of slavery -- both temporary bondage for debt applied to fellow Israelites, and straightforward chattel slavery applied to non-Israelites.
Now, such laws should, I think, be evaluated in light of standards prevailing internationally when they were adopted. For example, the law that allows an engaged woman who has sexual relations with someone other than her fiancé to be stoned at her parents' doorstep should be evaluated in light of the honor killings that are associated with middle eastern tribal cultures to this day. Likewise, the laws regarding stoning of rebellious sons should be seen in light of the widespread concept of the head of a family having life and death power over its members. Back in the early iron age, a law saying that a man needed the consent of the town elders, a court order, to kill his slut of a daughter or his disobedient son (and that he couldn't deliberately kill his slacker slave at all!) must have aroused dark mutterings about nanny-state interference with parental rights.
But that's not quite Ray's approach. On the one hand, he can't raise the arguments that the Mosaic law represented incremental ameliorations of tribal customs (much less that it represented a series of them over time: that the law was not given all at one time but evolved); he has to present a case that this was a perfect law code given by a perfect God. On the other, he really doesn't seem enthusiastic about the merits of capital punishment for gays or atheists or pagans or misbehaving teens or even Muslims. He argues that there's no biblical evidence that most of these death penalties were ever applied. Harsh penalties, he states, work well to discourage people from committing the offense.
This is a rather odd argument. Even if Ray has never heard Samuel Johnson's anecdote about seeing pickpockets working the crowd at the hanging of a pickpocket, or considered the honor killings that go on today in the Middle East (where girls know perfectly well that such things happen), he ought to consider the sheer number of unrepentant "false converts" and non-converts that he claims know that God exists and that Hell awaits the unrepentant. Eternal fiery torment is just about as harsh a penalty as ever focussed a man's mind, and it plainly is less than 100% effective. He ought, on that ground, conclude that the ancient Israelites were probably stoning adulteresses, homosexuals, and rebellious sons fairly frequently, whether the Bible mentioned this or not. The problem is that his theology tells him that God's law -- even "ceremonial" and "civic" laws no longer in effect, as well as a "moral" law that it -- must be perfect, objective, and absolute, and his conscience tells him that it isn't.