Think of the catalyst as the "unfinished" masterwork. Once you get the catalyst for that weapon, you then have to fulfill the unique requirements listed for that weapon, in order to unlock the full benefits of that weapon, thus, turning that catalyst into the masterwork. Once the masterwork is fully unlocked, the benefits will be permanent. Even if you delete the weapon and buy it again from your collection, the masterwork is still unlocked and intact.
I posted a screenshot on a previous page of what a finished exotic masterwork looks like. The gold border and ornamentation on the banner appears once the masterwork is fully unlocked and applied.
The Vigilance Wing catalyst randomly drops in Crucible. Once obtained, you must get 5 blood for blood medals AND 250 kills with the weapon (again, assists, super, grenade and melee kills do not count). This is just for Vigilance Wing. Other weapons have different criteria for their masterwork.
Once that is done, the master work is unlocked and the weapon is increased benefits. For Vigilance Wing, it recieves full auto firing.