How do those who follow Sola Scriptura and who don’t have a Confession or Article of Faith decide what is or is not heresy?
The following is the Common Christological Declaration between the Catholic Church and the Assyrian Church of the East, formerly referred to colloquially as the “Nestorian Church.”
COMMON CHRISTOLOGICAL DECLARATION
BETWEEN THE CATHOLIC CHURCH
AND THE ASSYRIAN CHURCH OF THE EAST
His Holiness John Paul II, Bishop of Rome and Pope of the Catholic Church, and His Holiness Mar Dinkha IV, Catholicos-Patriarch of the Assyrian Church of the East, give thanks to God who has prompted them to this new brotherly meeting.
Both of them consider this meeting as a basic step on the way towards the full communion to be restored between their Churches. They can indeed, from now on, proclaim together before the world their common faith in the mystery of the Incarnation.
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As heirs and guardians of the faith received from the Apostles as formulated by our common Fathers in the Nicene Creed, we confess one Lord Jesus Christ, the only Son of God, begotten of the Father from all eternity who, in the fullness of time, came down from heaven and became man for our salvation. The Word of God, second Person of the Holy Trinity, became incarnate by the power of the Holy Spirit in assuming from the holy Virgin Mary a body animated by a rational soul, with which he was indissolubly united from the moment of his conception.
Therefore our Lord Jesus Christ is true God and true man, perfect in his divinity and perfect in his humanity, consubstantial with the Father and consubstantial with us in all things but sin. His divinity and his humanity are united in one person, without confusion or change, without division or separation. In him has been preserved the difference of the natures of divinity and humanity, with all their properties, faculties and operations. But far from constituting “one and another”, the divinity and humanity are united in the person of the same and unique Son of God and Lord Jesus Christ, who is the object of a single adoration.
Christ therefore is not an “ ordinary man” whom God adopted in order to reside in him and inspire him, as in the righteous ones and the prophets. But the same God the Word, begotten of his Father before all worlds without beginning according to his divinity, was born of a mother without a father in the last times according to his humanity. The humanity to which the Blessed Virgin Mary gave birth always was that of the Son of God himself. That is the reason why the Assyrian Church of the East is praying the Virgin Mary as “the Mother of Christ our God and Saviour”. In the light of this same faith the Catholic tradition addresses the Virgin Mary as “the Mother of God” and also as “the Mother of Christ”. We both recognize the legitimacy and rightness of these expressions of the same faith and we both respect the preference of each Church in her liturgical life and piety.
This is the unique faith that we profess in the mystery of Christ. The controversies of the past led to anathemas, bearing on persons and on formulas. The Lord’s Spirit permits us to understand better today that the divisions brought about in this way were due in large part to misunderstandings.
Whatever our Christological divergences have been, we experience ourselves united today in the confession of the same faith in the Son of God who became man so that we might become children of God by his grace. We wish from now on to witness together to this faith in the One who is the Way, the Truth and the Life, proclaiming it in appropriate ways to our contemporaries, so that the world may believe in the Gospel of salvation.
http://www.vatican.va/roman_curia/pontifical_councils/chrstuni/documents/rc_pc_chrstuni_doc_11111994_assyrian-church_en.html
for them it becomes a case of burning in the bosom. The problem lies in that people think they can just pick up, thumb a verse and build a philosophy. God did not give us a Book, He gave us His living Word and He gave us a community to learn and pray together. Together as a community riles many who take individualism to extremes