My Summary of Christian Doctrine: The Trinity Second Part.

The Trinity Second Part.Those who deny This Doctrine of the Scriptures.

This doctrine was denied by the Socinians in the Days of the Reformation.

Michael Servetus was a 16th century Spanish theologian, physician, cartographer, and Renaissance humanist. He was a polymath versed in many sciences: mathematics, astronomy and meteorology, geography, human anatomy, medicine and pharmacology, as well as jurisprudence, translation, poetry and the scholarly study of the Bible in its original languages. The writings of Servetus laid the foundations for the Socinian movement

http://www.socinian.org/

Socinianism (pronunciation: /səˈsɪniːənizm/) is a system of Christian doctrine named for Fausto Sozzini (Latin: Faustus Socinus), which was developed among the Polish Brethren in the Minor Reformed Church of Poland during the 16th and 17th centuries and embraced by the Unitarian Church of Transylvania.

The Trinity is also denied by the Unitarians and Modernists of our day.

Unitarianism is a Christian theological movement named for the affirmation that God is one entity, in direct contrast to Trinitarianism, which defines God as three persons in one being.[1] Unitarians maintain that Jesus of Nazareth is in some sense the "son" of God (as all humans are children of the Creator), but that he is not the one God himself. [2] They may believe that he was inspired by God in his moral teachings and can be considered a saviour,[3] but all Unitarians perceive Christ as human rather than divine. Unitarianism is also known for the rejection of several other Western Christian doctrines,[4] including the soteriological doctrines of original sin and predestination,[5][6] and, in more recent history, biblical in-errancy.[7] Unitarians in previous centuries accepted the doctrine of punishment in an eternal hell, but few do today. Wikipedia.com

Modernism refers to theological opinions expressed during the late 19th and early 20th centuries, but with influence reaching into the 21st century, which are characterized by a break with the past. Catholic modernists form an amorphous group. The term "modernist" appears in Pope Pius X's 1907 encyclical Pascendi dominici gregis.[1] Modernists, and what are now termed "Neo-Modernists", generally do not openly use this label in describing themselves. Traditionalist Catholics, however, continue to use the term.

Modernists came to prominence in French and British intellectual circles and, to a lesser extent, in Italy.[2] The Modernist movement was influenced by Protestant theologians and clergy, starting with the Tübingen school in the mid-19th century. Some modernists, however, such as George Tyrrell, would disagree with this; Tyrrell saw himself as loyal to the unity of the Church, and disliked liberal A rationalistic approach to the Bible. The rationalism that was characteristic of the Enlightenment took a proto-materialistic view of miracles and of the historicity of biblical narratives. This approach sought to interpret the Bible by focusing on the text itself as a prelude to considering what the Church Fathers had traditionally taught about it. This method was readily accepted by Protestants and Anglicans. It was the natural consequence of Martin Luther’s sola scriptura doctrine,[citation needed] which asserts that Scripture is the highest authority, and that it can be relied on alone in all things pertaining to salvation and the Christian life.

Secularism and other Enlightenment ideals. The ideal of secularism can be briefly stated as follows: the best course of action in politics and other civic fields is that which flows from a common understanding of the Good by various groups and religions. By implication, Church and State should be separated and the laws of the latter, for example that forbidding murder, should cover only the common ground of thought systems held by various religious groups. From the secularists’ point of view it was possible to distinguish between political ideas and structures that were religious and those that were not, but Catholic theologians in the mainstream argued, following St. Thomas Aquinas, that such a distinction was not possible: All aspects of society were to be organized with the final goal of Heaven in mind. However, the humanist model which had been in the forefront of intellectual thought since the Renaissance and the scientific revolution was directly opposed to the Thomist view. Wikipedia.com]

The Arian Controversy.

The Arian controversy was in reality a series of controversies, related to Christology, that arose between Arius, a priest and theologian, and Bishop Athanasius, a Church Father. The most important of these controversies concerned the substantial relationship between God the Father and Jesus Christ. These disagreements divided the Church into two opposing theological factions for over 55 years, from the time before the Council of Nicaea in 325 until after the Council of Constantinople in 381. There was no formal schism; the matter remained an internal conflict of the Church. Wikipedia.com

This is the doctrine espoused by the Jehovah's Witnesses saying that Jesus Christ is not divine but just a man.

Those who reject the Trinity such as the Unitarians or Modernists of our own day, If they refer to the trinity at all, they represent it as consisting of the father, the man Christ Jesus, and the divine influence  which is called the Spirit of God.  L.B. P. 43