A chieftain or if you were reading it in Icelandic, goði (gothi) were more religious leaders when the Vikings still practiced heathenism and also a tribal community leader. Since most Norseman lived on farm estates with other people including kin and thalls (slaves) the chieftain was the wealthiest and most respected of the group to be given the honor of proceeding over festivals, feasts, rituals and maintaining the communal hall (hof). In Iceland during the Commonwealth period, each community had a goði that represented them at the Althingi meetings.

Now Jarls (Earls) have a regal and more legal connotation separate from goði but there are instances of Jarls functioning as religious leader as well. Before the unification of Norway each region was ruled over by a petty king, afterwards it was useful in an age where travel and communication were slower to have official agents carrying out the kings orders directly, thus Jarls were the next level under a king. They had the right to collect taxes (and give a cut to the king) and create a hird (a personal military retinue). Jarls also had a voice in deciding who the defacto king would be during succession periods On Orkney Island, the Jarl was the head honcho under the Norwegian king but since there were communities under the Jarl there were also goði that acted as the heads of their community.

Therefore not all chieftains are jarls but a jarl could be a chieftain over their own local community.

There may be a few other nuances that I cannot recall right now but I believe that is the gist of it.