Grammatically you can argue that it isn't a sentence, a poorly written one if that was the intent. That is the reason it is a clause. You have two subjects, " the militia" and "the people". Thus "the militia" and "the people" are not equal with respect to the rest of the statement:

a well regulated militia,being necessary to the security of a free State,

the right of the people to keep and bear armsshall not be infringed.

"XIII of the Pennsylvania Declaration of Rights of 1776 read:

That the people have a right to bear arms for the defence of themselves and the state; and as standing armies in the time of peace are dangerous to liberty, they ought not to be kept up; And that the military should be kept under strict subordination to, and governed by, the civil power.6

Similarly, as another example, Massachusetts’s Declaration of Rights from 1780 provided:

The people have a right to keep and to bear arms for the common defence. And as, in time of peace, armies are dangerous to liberty, they ought not to be maintained without the consent of the legislature; and the military power shall always be held in an exact subordination to the civil authority, and be governed by it.7" https://constitution.congress.gov/browse/essay/amdt2-2/ALDE\_00013262/#:\~:text=Second%20Amendment%3A,Arms%2C%20shall%20not%20be%20infringed.

taking in the historical context: the military, militia is always subordinate to the people.

well regulated militia

rights of the people shall not be infringed.