I am working on a very basic article on Paul and the law in Galatians and I wanted to offer a simple analogy which would represent both the positive aspects of the law and also why Paul was so concerned that his converts don’t slavishly (!) try to obey the Mosaic Law for justification. Here it is: (I encourage feedback, but be aware that any illustration is going to be limited and only offer insight into one or two areas. Also, I want to keep it simple!)
Imagine that Israel is like a car going on a trip. Sin is like a rusty nail that punctured a tire and Israel is slowing down even to the point that the flat tire is doing some damage to the car. The spare tire is like the Mosaic Law- a gift! Something that will enable Israel to make the car drivable and to get to a safe place (using backroads, of course). The car is ‘whole again’ with the spare tire (the Law). But – a spare tire, for how useful and necessary it is, IS A TEMPORARY SOLUTION! In fact, once you have driven the 50 miles that the spare is built for, if you continue on with it, it has become a liability and will eventually place you in a dangerous situation. Also, a spare tire (the Law) is not meant to go on highways and drive at higher speeds – it has a limited usefulness, though it is necessary. If the car (Israel) wants to complete its trip, it must have a new tire so it can get back on the highway…
The problem with Israel was that she was guarding and encouraging the ongoing use of the spare tire, even when the new tire had been acquired (‘when the time had fully come…’). But because Israel had to get off of the highway to the destination and take backroads for safety, she was never going to get there without doing what was necessary to make highway driving possible again. So, while the spare tire (as a concept) is both good and necessary, it fulfilled its purpose in the PAST and to force the continual use of it past its intended travel time is dangerous and counter-productive.
[There are lots of thorny issues about why the law is dangerous (see Philippians 3), but this analogy gets at the heart of the eschatological problems with the law. I am influenced by Richard Hays in his work on this subject, though I think Wright would conceive of this similarly]