But this you have, that you hate the works of the Nicolaitans, which I also hate. -- Revelation 2:6
So you also have some who hold to the teaching of the Nicolaitans in the same way. -- Revelation 2:15.
Streeter states in his book "The Revelation of Jesus Christ":
There is quite a general agreement among expositors concerning what Nicolaitanism is. It is interesting to observe that it was a thing that started in Ephesus in practice, and afterwards embodied itself in theory; and finally in Pergamos it is mentioned as becoming a feature of doctrine, and the Savior thus again expresses Himself concerning it: "So in like manner thou hast also those holding the teaching [doctrine] of the Nicolaitans." (Rev. 2:15.) It has been forcefully described as "something which put down the people [of God], superseded them in their rights, and set them aside; for this is the plain import of the name, which Christ gives it, and the names which are divinely given are always exactly descriptive of the things or persons that receive them. We also know from the Scriptures and from the common representations of all ecclesiastical historians that the Church was hardly founded until it began to be troubled with the lordly pretensions and doings of arrogant men in violation of the common priesthood of believers, and settling upon ministers the attributes and prerogatives of a magisterial order against which Peter, Paul, and John were moved to declare their apostolic condemnation, but which grew nevertheless and presently became fixed upon the [professed] Church as a part of its essential system. We know that there is to this day a certain teaching and claim and practice in the largest part of the professed Church according to which a certain order severs itself entirely from the laity, assumes the right and titles of priesthood, asserts superiority and authority over the rest in spiritual matters, denies the right of any one, whatever his gifts or graces, to teach or preach in the Church, who has not been regularly initiated into the mysterious puissance of its own self-constituted circle, and puts forward its creatures (however glaringly deficient in those heavenly gifts which really make the minister), as Christ's only authorized heralds, before whom every one else must be mute and passive and whose words and administrations every one must receive, on pain of exclusion from the hope of salvation [or of losing their crown].
"We also know that this system of priestly clericalism and prelatical hierarchism claims to have come down from the earliest periods of the Church, and traces for itself a regular succession through the Christian centuries, and appeals to patristic practice as its chief basis, vindication, and boast. We know that it first came into effective sway in the period immediately succeeding the Pagan persecutions, reaching its fullest embodiment in Popery, and has perpetuated itself in the same, and in Laudism, Tractarianism, and Highchurchism, even to our day, and to our very doors. And if we would know what the Lord Jesus thinks of it, we have only to recur to these epistles, in which He lays His hand right on it, and says: 'This Thing I Hate.'"
Charles T. Russell's views were in full accordance with the foregoing presentation; his clear statement was:
The 'doctrine of the Nicolaitans' seems to be the theory of lordship or headship in the Church. The strife as to who should be greatest existed amongst many of the patriarchs -- fathers -- of the prominent churches. At their councils there was a bitter fight for supremacy. The tendency was toward an earthly head, and of course many coveted the honor. The patriarchs of Jerusalem, Antioch, Constantinople, and Rome were the most prominent. The first two dropped out of the conflict, but the strife continued for several hundred years between Constantinople and Rome. It was settled only by a division of the Church: the Eastern, or Greek Church, accepting the Patriarch of Constantinople for its head; and the Western, or Papal Church, acknowledging the Bishop -- Pope or Father -- of Rome.
Many of the true followers of the Master in the churches denounced this attempt to disobey the direct command of Jesus, 'Call no man Father.' (Matt. 23:9.) Of course, they received the promised persecution. (2 Tim. 1:12.) This class in Pergamos is commended by our Lord under the symbol of 'Anti-pas, My faithful martyr.' In the Greek, anti means against, and papas signifies father. In this stage of the development of the Church those who sought to be popular received the emoluments of the Church; but the promise to the overcomers is that of pleasure and honor that shall be eternal.
Nicolaitanism was only in its incipiency when mentioned in the message to Ephesus. It, as we have seen, became a doctrine in Pergamos. The evil of "Nicolaitanism" has always existed in the Church since shortly after its establishment. Every reform movement in the Church since the Apostles' day--every effort to get back to primitive simplicity of doctrine, of church order, and of methods of service, has, in the course of time, resulted again in sectarianism, and has left the faithful few (Protestants) in the "wilderness." Lording it over God's heritage, idolizing messengers and human organizations, symbolized by "Nicolaitanism," is responsible for these sad results. This evil has been repeated again and again in the Church's history. Even in the very closing hours of the Church's pilgrimage we are witnessing its repetition. Let him that readeth understand! How necessary, how significant, how timely the Savior's warning: "Take heed, let no man deceive you." The worshipping of fallible men, the worshipping of imperfect human systems--making idols of them, allowing them to occupy the place that Christ and Christ alone should occupy, has ever been Satan's method of taking away the liberty that is in Christ Jesus, and thus of marring the fellowship and destroying the unity of "the Church of the living God, the pillar and ground of the Truth."
Frank Shallieu, in his book on Revelation states:
The “doctrine of the Nicolaitans” is related to former Amazonic worship, which was designed to tempt one’s ego with power, influence, and leadership. The Nike goddess of victory is found amid the Pergamon statuary. This goddess invariably has one breast exposed not so much to denote femininity but to point her out as the provider of nutriment for overcoming strength and resultant victory.
First noticed in Ephesus, the doctrine of the Nicolaitans, the theory of lordship or headship in the Church, found its development in Pergamos and has been a burden ever since. In Ephesus it was designated “the deeds of the Nicolaitans,” that is, a tendency towards lordship in the Church; in Smyrna there emerged an organization of believers referred to as “the synagogue of Satan”; now in Pergamos that which should never have been tolerated — which the Ephesian Church abhorred — became an established and recognized doctrine: clericalism.
It seems they were conquering the people with pagan doctrine as Strongs also refers to them as heretics, as they were connected with worhsip of Greek gods and their customs that involved lordship, idolatry and sectarianism.