Upvote:4
That phrase was written both as a condemnation of individuals within the Church, and religious groups that maintained that Jesus Christ was "of another substance or essence". As you rightly point out, the controversy revolved around the meaning of Greek words. Although the 325 Nicene Creed tried to clarify, so as to prevent people twisting words to allow them to remain within the Church despite holding to unorthodox beliefs about Christ, it did not succeed. More problems arose later, continuing such arguments about words. Let me quote from this scholarly book dealing with this troubled time in the Church.
"While Athanasius was in exile in Trier, Arius died - one day before he was to be restored as a Christian presbyter in a special ceremony in Constantinople in 336, only months before Constantine's own death on May 22, 337. Constantine lived as a pagan and died as an Arian... > Constantine's successor was his son Constantius... who ruled until his death in 362, [and] constantly hounded the bishop [Athanasius] who seemed the last key holdout for trinitarian orthodoxy against Arianism and semi-Arianism. The emperor wanted peace, and uniformity was it> path, [wanting to] replace h*m*ousios in the Nicene Creed with h*m*iousios which means, 'of a similar substance' and would be acceptable to the semi-Arians...
"In all, Athanasius endured five exiles.' Seventeen years, out of forty-six as bishop, Athanasius had spent in exile. Politics and theology had ever intermingled...' 7... His own synod in Alexandria met in 362. The bishops gathered there reaffirmed h*m*ousios as the only proper description of the relationship of the Son of God to the Father and explicitly rejected both the semi-Arian h*m*iousios and Sabellianism as heresies... Athanasius died in 373 in Alexandria."
As the Council of Constantinople adjourned and the bishops departed for their home sees, the differences and resentments between Alexandria and Antioch were just beginning to boil... The Council of Constantinople had made official the use of terms and concepts like nature and person for explaining the Trinity. Alexandrians... would argue more and more vehemently that just as the Trinity is one substance, or nature, and three persons so Jesus Christ is one nature and one person... When it comes to personhood, Antiochenes averred, two can become one while remaining two. The stage was set for a theological blowout... [which] came in 428." The Story of Christian Theology, Roger E. Olson, pp 164-166, 197 & 210 (Apollos 1999)
My answer to your question is that the Nicene Creed was using words to convey the belief that just as the Father is of divine essence, so the Son of God is of the same divine essence. In other words, the Son is not another God. Whatever God consists of, the Son consists of. And as God the Father is true God, so the Son also is true God, and not a lesser god. The deity of the Son is just as total as the deity of the Father.