The Crucian knights were Ba'al's forces on Atraxia. They infiltrated the planet's culture while Sokar ruled it. They maintained control on Ba'al's behalf and used their influence for when he would arrive, he would be greeted as the divinity he would claim to be.
Only Jaffa loyal to Ba'al were permitted to join the order. While membership was quite limited, each monastery could call upon able bodied men of the local village at will. (RPG: "Living Gods: Stargate System Lords")