Well, the title pretty much sums it up. Occupation followed by desired acquisition.
Thief, conceptually is a simple game. Load level, steal stuff, get out. For the time period that this game came out, it made a lot of thief tools available to you that not every stealth game (not that there were an abundant of them) was necessarily providing at the time. You can avoid bloody messes by knocking people out. You can drag bodies to hide them. You can walk on soft surfaces to hide your footsteps. You can hide in the shadows. If being a thief is your role-playing thing, then this game is completely tailored to providing you that experience.