In Roman religion the gods' primary function was to?

Their primary function was to teach lessons and give examples of how one should live. In a monotheistic religion (Christianity) the sole god passes all judgments, creates all living things, and gives all lessons. In the case of Christianity these lessons come from Jesus and from stories like noahs arc which are human stories.

The roman stories of the gods were different, and they did not portray all of the gods in the shining white light and purity of the christian faith.

Jupiter(Zeus in the greek) was an unfaithful husband to Juno(Hera in the greek). Her wroth at his infidelity was terrible to behold, and she ever sought to get even with him.

Giving the gods these human characteristics and imperfections made them better teachers of lessons, and therefore that is their purpose: To be examples to mankind, of how to behave and the consequences of their behavior, and also to explain some natural phenomena for which there was no scientific answer at the time (Juno's thunderbolts, and not electrical discharge, were credited for making lightning appear, etc etc.)