From the web site.

The word necessary appears in the Bill of Rights only one time.

Why is the second amendment necessary? This is the only instance in which the Constitution explicitly specifies anything in particular as “necessary” for any particular purpose, and inasmuch as the absolute clause “[a] well regulated Militia, being necessary to the security of a free State” is couched in the present tense, the Constitution obviously considers “the security of a free State” to be a permanent goal, and “[a] well regulated Militia” to be the one and only means truly “necessary” to achieve that goal at all times and under all circumstances. That is, “the security of a free State” and “[a] well regulated Militia” are mutually inseparable and constitutionally indispensable.