The changes read (additions marked in bold, deletions in strikeout):

That the right of every citizen to keep and bear arms, ammunition, and accessories typical to the normal function of such arms, in defense of his home, person, family and property, or when lawfully summoned in aid of the civil power, shall not be questioned; but this shall not justify the wearing of concealed weapons. The rights guaranteed by this section shall be unalienable. Any restriction on these rights shall be subject to strict scrutiny and the state of Missouri shall be obligated to uphold these rights and shall under no circumstances decline to protect against their infringement. Nothing in this section shall be construed to prevent the general assembly from enacting general laws which limit the rights of convicted violent felons or those adjudicated by a court to be a danger to self or others as result of a mental disorder or mental infirmity.

This makes Missouri the second state — after Louisiana — to provide for “strict scrutiny” of gun restrictions, generally thought to be the strongest level of protection (though even so, not absolute, see, e.g., this Louisiana Supreme Court decision).

At this point, 42 states have constitutional right-to-bear-arms provisions that are either expressly worded as protecting an individual right — not subject to any of the disputes that have swirled around the Second Amendment — or that have been so interpreted by state courts. The remaining states are California, Iowa, Maryland, Minnesota, New Jersey, and New York (no such constitutional provision), Massachusetts (provision interpreted as only a “collective rights” provision, whatever that might mean in a state constitution), and Hawaii (provision tracks the Second Amendment, and hasn’t been definitively interpreted by state courts). I’m surprised that there hasn’t been a movement to add such a provision to the Iowa and Minnesota Constitutions, given that those are generally seen as pro-gun-rights states. In the last 30 years, 13 state right-to-bear-arms provisions have been created (Delaware, Nebraska, North Dakota, West Virginia, Wisconsin), shifted to clear individual rights provisions (Alaska, Kansas, Maine), or strengthened (Florida, Louisiana, Missouri, New Mexico, Utah).