The first Texas State Constitution was drafted in 1845, right after we entered the Union, and amended in 1861 when we seceded, naming Texas as a State of the Conferacy.
It was once again re-written in 1866 (after the Civil War) establishing that Texas was "rejoining" the United States of America.
The Republican Party Reconstructionists (Carpetbaggers) changed it in 1869 to better suit their own political needs, since they were in control at the time.
Then it was changed again when local Democrats regained control of State government from the Davis regime. (Davis had been appointed Texas' Governor by the President, and had to be physically forced from the State Capital at gun point by a mob of Texas Democrats after the first allowed election after the war)
The 1875 re-write/amended version is the one Texas currently utilizes, however it has been amended over a hundred times, just since the 1875 version was enacted.
(Ours is the most confusing State Constitution in United States history, just due to Texas first being a Republic, then a State, then seceding to become a State in the Confederacy, and then entering the Union as State again)
Texas civilians after the war were treated pretty badly under martial law. Some Davis appointees ransomed bounties from cities and town, offering to lift martial law if certain fees were paid.
Gonzales, Texas had that happen, and one of their disgruntled citizens was a guy named John Wesley Hardin. He had fought in the war, and hated the fact that yankee soldiers, and yankee appointees to the State Police were in charge of law enforcement in Texas. As a matter of fact, the majority of Hardin's shooting victims were State Police Officers and U.S. Army Soldiers in the beginning of his outlaw "career".
I think the reason that law was enacted, may well have been Texans at that time wanted the right of the People to keep and bear arms, but just didn't want "Union Sympathizing Carpetbaggers" to be able to shoot back.