Protostellar disks are a ubiquitous part of the star formation process and the future sites of planet formation. We present high angular resolution dust continuum and molecular line observations from the Early Planet Formation in Embedded Disks (eDisk) large program of the young, Class 0 protostar, IRAS 15398-3359. The dust continuum traces a large-scale structure within the bipolar outflows as also seen in previous observations of this source, while the higher angular resolution image reveals a compact continuum structure (4.5au x 2.8au). The molecular lines of C18O (J=2?1), 13CO (J=2?1), 12CO (J=2?1) and SO (J_N=6_5-5_4) are all detected and trace components of the protostellar disk, infalling-rotating envelope, and bipolar outflows. We analyze and fit the position-velocity (PV) diagrams of the SO emission with a power-law rotation profile and find a power-law index closer to -1.0, indicative of infall with conserved angular momentum. When fitting only higher velocity points, the power-law index flattens out closer to -0.5, indicating the presence of a Keplerian rotating disk. We estimate the protostellar mass is likely somewhere between 0.022Msun-0.045Msun, and a small gas disk with radius <30au. Our results highlight the importance of high spatial and spectral resolution observations to trace small protostellar disks in the very early stages of low-mass star formation.