The Second Amendment reads as follows:
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
This can be neatly divided into two parts, split after the word "State", in which the second half would be merely an explicit statement of the law. The question, though, is what is the purpose of the first half?
From what I have seen, it seems that there are two main viewpoints. One view assumes that the first half is a limitation on the explicit law in the second half, in which the right to keep and bear arms is in some way limited to something related to a militia or security of a state. The other view assumes that the first half is not a limitation on the right in the second half, but some kind of introduction or statement of purpose or motivation.
I don't really understand either of these options. If the first half is intended to be part of the law, why not write it explicitly? Something like the right to keep and bear arms to maintain a militia shall not be infringed. If the first half is not intended as part of the law itself, why is this the only constitutional amendment with such an introductory clause?
I have seen several questions on this site that relate to the wording of the Second Amendment, but they all just discuss what the intent (or the law) of the amendment actually is. This question is not about what the amendment actually allows or limits, but about the reason for its unique written structure.