In ancient Rome – really, the whole ancient world – participation in public or national festivals centered around idol worship, including sexual immorality and eating things sacrificed to idols.

“Religion in ancient Rome encompasses the ancestral ethnic religion of the city of Rome that the Romans used to define themselves as a people, as well as the adopted religious practices of peoples brought under Roman rule. The Romans thought of themselves as highly religious, and attributed their success as a world power to their collective piety (pietas) in maintaining good relations with the gods. According to legendary history, most of Rome’s religious institutions could be traced to its founders, particularly Numa Pompilius, the Sabine second king of Rome, who negotiated directly with the gods. This archaic religion was the foundation of the mos maiorum, ‘the way of the ancestors’ or simply ‘tradition’, viewed as central to Roman identity. The priesthoods of public religion were held by members of the elite classes. There was no principle analogous to ‘separation of church and state’ in ancient Rome. During the Roman Republic (509–27 BC), the same men who were elected public officials might also serve as augurs and pontiffs. Priests married, raised families, and led politically active lives. Julius Caesar became Pontifex Maximus before he was elected consul. … The Roman triumph was at its core a religious procession in which the victorious general displayed his piety and his willingness to serve the public good by dedicating a portion of his spoils to the gods, especially Jupiter, who embodied just rule.”

“Religion in Ancient Rome,” Wikipedia.

“Festivals in ancient Rome were an important part of Roman religious life during both the Republican and Imperial eras, and one of the primary features of the Roman calendar. … State holidays were celebrated by the Roman people and received public funding.”

“Roman Festivals,” Wikipedia.

Christine’s comment: Reviewing both articles shows the extent to which public holidays were both religious and national in character. The attendant rites which accompanied pagan idolatry, including animal sacrifice, were integral to the celebrations. This practice did not begin with Rome, but had come down from the original corruption of religion at Babel.

See these related posts for detail:

Public Celebrations in Pagan Idolatry
Immorality & Sacrifices Integral to Pagan Idolatry

Nicolaitans were disciples of the deacon Nicolaus, and while not much is known of them from Scripture, the writings of the early church fathers mention them. They were said to lead lives of unrestrained indulgence …

“Irenaeus (Adv. Hoeres. i. 26) says that their characteristic tenets were the lawfulness of promiscuous intercourse with women, and of eating things offered to idols. Eusebius (Hist. Eccl. iii. 29) states substantially the same thing … Tertullian speaks of the Nicolaitanes as a branch of the Gnostic family, and as, in his time, extinct.”

Albert Barnes, Notes on … Revelation, p. 67.

“The Nicolaitans are mentioned as a licentious sect in the Rev 2:6, 2:15. They claimed as their founder Nicolaus, a proselyte of Antioch and one of the seven deacons of the congregation of Jerusalem (Act 6:5). … But the views of the fathers are conflicting. Irenaeus (who is followed substantially by Hippolytus) gives a very unfavorable account. ‘The Nicolaitanes,’ he says, ‘are the followers of that Nicolaus who was one of the seven first ordained to the diaconate by the apostles. They lead lives of unrestrained indulgence. The character of these men is very plainly pointed out in the Apocalypse of John, where they are represented as teaching that it is a matter of indifference to practice adultery, and to eat things sacrificed to idols. Wherefore the Word has also spoken of them thus: “But this thou hast, that thou hatest the deeds of the Nicolaitanes, which I also hate.”’ Clement of Alexandria says that Nicolaus was a faithful husband, and brought up his children in purity, but that his disciples misunderstood his saying (which he attributes also to the Apostle Matthias), ‘that we must fight against the flesh and abuse it.’”

Philip Schaff, History of the Christian Church, Vol. 2, p. 416.

“Ephesus—famed for the temple of Diana, one of the seven wonders of the world. For three years Paul labored there. He subsequently ordained Timothy superintending overseer or bishop there: probably his charge was but of a temporary nature. John, towards the close of his life, took it as the center from which he superintended the province.”

Jamieson, Faussett, and Brown’s Commentary, “Revelation chapter 2.”

The LORD opens every letter to the seven churches the same way: “I know your works.”

“Each of the seven epistles in this and the third chapter, commences with, ‘I know thy works.’ Each contains a promise from Christ, ‘To him that overcometh.’ Each ends with, ‘He that hath an ear, let him hear what the Spirit saith unto the churches.’”

Jamieson, Faussett, and Brown’s Commentary, “Revelation chapter 2.”