Sexual immorality and eating things sacrificed to idols were part and parcel of pagan idolatry.

“The special enticements to idolatry as offered by these various cults were found in their deification of natural forces and their appeal to primitive human desires, especially the sexual … Baal and Astarte worship, which was especially attractive, was closely associated with fornication and drunkenness (Amos 2:7 , Amos 2:8; compare 1 Kings 14:23 f), and also appealed greatly to magic and soothsaying (e.g. Isaiah 2:6; Isaiah 3:2; Isaiah 8:19 ).”

“Idolatry,” International Standard Bible Encyclopedia.

“It seems strange to a modern reader that with these ceremonial prohibitions [against idolatry] should be connected the strictly moral prohibition of fornication. … no heathen moralist, not even Socrates, or Plato, or Cicero, condemned fornication absolutely. It was sanctioned by the worship of Aphrodite at Corinth and Paphos, and practiced to her honor by a host of harlot-priestesses! … Hence the author of the Apocalypse also closely connects the eating of meat offered to idols with fornication, and denounces them together.”

Philip Schaff, History of the Christian Church, Vol. 1, pp. 294.

“Ancient Near Eastern societies … featured many shrines and temples or ‘houses of heaven’ dedicated to various deities. According to the 5th-century BC historian Herodotus, the rites performed at these temples included … what scholars later called sacred prostitution. … The Hebrew Bible uses two different words for prostitute, zonah (זנה)‎ and kedeshah (or qedesha) (קדשה)‎. The word zonah simply meant an ordinary prostitute or ‘loose woman’. But the word kedeshah literally means ‘consecrated’ (feminine form), from the Semitic root q-d-sh (קדש)‎ meaning ‘holy’ or ‘set apart’. Whatever the cultic significance of a kedeshah to a follower of the Canaanite religion, the Hebrew Bible makes it clear that cultic prostitution had no place in Judaism. Thus the Hebrew version of Deuteronomy 23:17-18 tells followers: ‘None of the daughters of Israel shall be a kedeshah, nor shall any of the sons of Israel be a kadesh. You shall not bring the hire of a prostitute (zonah) or the wages of a dog (kelev) into the house of the Lord your God to pay a vow, for both of these are an abomination to the Lord your God.’ Stephen O. Murray writes that biblical passages ban qdeshim and link them with gods and ‘forms of worship detested by orthodox followers of Yahweh’.”

“Sacred Prostitution,” Wikipedia.

Public holidays in the ancient world were both religious and national in character. The attendant rites which accompanied pagan idolatry, including animal sacrifice, were integral to the celebrations. This practice had come down from the original corruption of religion at Babel.

“Nimrod, being the founder of both their civilization and their religion, served as king, and chief priest. The later kings of Sumer (as Shinar is known today) followed his example in this, as in all else.”

Christine Miller, The Story of the Ancient World, p. 40.

“The ritual alone which accompanied divination practices and incantation formulae was a chief factor in the celebration of festival days …”

“Babylonian and Assyrian Religion,” The Encyclopaedia Britannica, Vol. 3, p. 115.

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.

The Unfolding Vision of Revelation
Revelation Repeats Old Testament Prophets
The Four Living Beings
Chiastic Structure
The Scroll of the History of the World
Lion of Judah, Root of David Previously Explained in Scripture
Revelation 4 Chiastic Structure
Revelation 5 Chiastic Structure