Which two issues were primarily addressed at the Council of Nicaea I?

The Council of Nicaea I, convened in 325 AD, primarily focused on addressing two significant issues: Arianism and the establishment of the date of Easter.

Arianism was a theological doctrine proposed by Arius that contended that Jesus Christ was not co-eternal with God the Father, implying that there was a time when Christ did not exist. This view challenged the understanding of the Trinity and the divine nature of Christ, leading to significant controversies within the early Christian community. The council definitively condemned Arianism and established the orthodox belief in the consubstantiality of the Son with the Father, affirming that Jesus is of the same substance as God, which was articulated in the Nicene Creed.

Additionally, the Council addressed the establishment of a universal date for Easter. The timing of the celebration varied significantly among different Christian communities, leading to confusion and disunity. The Council sought to create a uniform process for determining the date of Easter, which was established to fall on the first Sunday after the first full moon following the vernal equinox.

These decisions had far-reaching implications for the Christian faith's unity and doctrine, making this answer the most accurate representation of the key issues addressed during the Council of Nicaea