The recently discovered protostellar jet known as HH 212 is beautifully symmetric, with a series of paired shock knots and bow shocks on either side of the exciting source region IRAS 05413-0104. We present VLA ammonia maps of the IRAS 05413-0104 molecular gas envelope in which the protostellar jet source is embedded. We find that the envelope, with a mass of 0.2 M detected by the interferometer, is flattened perpendicular to the jet axis with an FWHM diameter of 12,000 AU and an axis ratio of 2 : 1, as seen in NH₃ (1, 1) emission. There is a velocity gradient of about 4-5 km s^-1 pc^-1 across the flattened disklike core, suggestive of rotation around an axis aligned with the jet. Flux-weighted mean velocities increase smoothly with a roughly constant velocity gradient. In young (class 0) systems such as HH 212, a significant amount of material is still distributed in a large surrounding envelope, and thus the observable kinematics of the system may reflect the less centrally condensed, youthful state of the source and obscuration of central dynamics. The angular momentum of this envelope material may be released from infalling gas through rotation in the HH 212 jet, as recent observations suggest. A blueshifted wisp or bowl of emitting gas appears to be swept up along the blue side of the outflow, possibly lining the cavity of a wider angle wind around the more collimated shock jet axis. Our ammonia (2, 2)/(1, 1) ratio map indicates that this very cold core is heated to 14 K in a centrally condensed area surrounding the jet source. This edge-on core and jet system appears to be young and deeply embedded. This environment, however, is apparently not disrupting the pristine symmetry and collimation of the jet.