How do people rationalize the cruelty of the Bible?

if god truly is all knowing and all seeing as they claim then there is no rational basis for any difference between his depiction in the old testament vs. the new testament. If he knows all then he could not have learned anything by the experience of "jesus" teaching him such basic concepts as "how to forgive". and there would be no reason why anything he made as "laws" in the old testament would no longer be relevant.