Final answer:
The First Council of Constantinople in 381 affirmed the Nicene Creed by declaring that the Holy Spirit should be worshiped and glorified alongside the Father and the Son, addressing the controversy of Arianism and contributing to the establishment of the doctrine of the Trinity.
Step-by-step explanation:
The council referred to in the question is the First Council of Constantinople of 381, which extended the Nicene Creed. This council is significant in Christian history because it emphasized the divinity of the Holy Spirit and its co-equal status with the Father and the Son, thus enhancing and refining the doctrine of the Trinity as we understand it in mainstream Christianity today. So, the council of Constantinople in 381 declared the Holy Spirit to be the Lord and giver of life, stating that like the Father and the Son, the Holy Spirit is to be worshiped and glorified. This decision was a critical response to Arianism, which had asserted Jesus Christ was subordinate to God the Father and that there was a time when He did not exist.
After the First Council of Nicaea in 325, which primarily addressed the nature of the Son in relation to the Father by refuting Arianism, the First Council of Constantinople expanded the church's dogma to include the Holy Spirit. The creed developed there, now part of the Nicene-Constantinopolitan Creed, addressed lingering Arian sentiments and other theological controversies. It was at this time that an official, unified doctrine was being formed in an attempt to maintain unity within the Christian Church amidst the diversity of beliefs and the rise of heresies that challenged established dogma. By declaring that the Holy Spirit was also worshiped and glorified together with the Father and the Son, the bishops at the council provided a clear plagiarism-free statement establishing the co-equality of the three persons of the Holy Trinity. This decision had a long-lasting impact on the doctrine and practice of most Christian denominations and was a key moment in defining the orthodoxy of the early Christian Church.