Old testament and new testament can be hard to reconcile for so many reasons, but I think one big reason is our misunderstanding of the concept of two different covenants. In the old testament, they had a specific covenant that God made and held to faithfully. When Jesus comes, there is a new covenant. This means we are no longer bound and under the agreements of the old covenant. So, for a short answer that’s why we don’t have to follow all the old testament laws because that was a part of a different covenant that we are not a part of. There is much more work that needs to be done here in explaining further but it’s just a reference point right now. This isn’t a perfect explanation or analogy, but I think it does provide some insight and give us a different way to look at how the new covenant is different from the old covenant and doesn’t ignore or reject or deny it but rather fully acknowledges and accepts it as it fulfills and transcends it.
Think of your relationship with your parents. When you were younger, you had really strict and rigid rules. A lot of times you didn’t understand them, and your parents hardly explained them (because you wouldn’t be able to understand) but you just had to follow them at their say so. I think it’s also critical to see that part of their rules system hardly allows for freedom for the child. There are extra rules in play that really are there just to prevent the child from even getting close to doing something bad because the parent doesn’t trust the child’s judgement or capability to be in certain situations without it ending up harmful. So, the parent puts in extra rules that in themselves don’t prevent us from doing harm but keep us at a safe distance from harm’s way. But just because those rules aren’t directly preventing us from something harmful and wrong, it would be ignorant and illogical to think we can break those rules without bringing about wrong or harm because our parents are the authority and we are under that must respect it.
However, when we get older, our parents trust us more and allow us more freedom and wiggle room. Not in the sense of deciding what’s right or wrong but in deciding how close can we get to right or wrong, or good or bad, without succumbing to harm or evil. The baseline of the right and wrong stays the same in principle, as in concept or thought, and also in rule. However, now that we have improved and have trustworthy judgement and thinking, we are allowed more autonomy in deciding what preventative rules are still necessary and useful for us and those which are not depending on how close we think we can stand next to the harm or wrong without being hurt or committing wrong. I think this is a fair way of looking at the old and new covenant in some respect. The old is when you’re young and the new is when you’re older. There are many other ways, and admittedly better ways to understand the relationship between the new and old testament, I think this is just one of many that helps us see how they are related.