When reading the message to the churches in Revelation, it becomes apparent that things have not changed much over time. That is the reason the message to the seven churches is as relevant today as it was almost 2,000 years ago.
Consider the female, Jezebel, who is associated with the church of Thyatira. In the Old Testament Jezebel was married to Ahab, king of Israel. She was a gentile and the daughter of Ethbaal, which means "Baal is alive." Baal was a false god worshipped by the Canaanites. Thus Ahab not only married a gentile in violation of God's command, but he also married into a family that worshipped a false deity.
Jezebel killed the prophets of God and stirred up Ahab to act wickedly before the Lord. (I Kings 18:4; 21:25) She was involved in harlotries that was part of Canaanite worship and participated in witchcraft. (II King 9:22) She was integral in influencing the entire nation of Israel to false worship through her husband Ahab.
The Jezebel in Revelation similarly led astray those of the church of Thyatira. She led God's servants to commit acts of immorality and to eat things sacrificed to idols. These were the very things that the Jerusalem council cautioned the Gentile believers to refrain from. (Acts 15) They were activities associated with pagan worship. But, she invented a way to bring the world into the church just as Jezebel did to Israel.
When the church strays from the clear teaching of God's word and overlooks 'minor' things to appease people, it opens the door for such evil as this. Most of the time it is a gradual process, a slow decay, that leads to such behavior. In the last fifty plus years many churches have drifted in their thinking. Within the church, living together (the Bible calls it fornication) has become almost as acceptable as marriage. And homosexual relationships are slowly being accepted as a God ordained union. It is obvious that this type of Jezebel spirit is just as alive today as it was in Thyatira. There are many in churches today seducing God's servants to commit acts of immorality.
He who is involved in such activity, God says "repent." He is very clear that all who practice such things will not inherit the kingdom of God. (Gal 5:21) The Lord "is longsuffering toward us, not willing that any should perish but that all should come to repentance." (II Peter 3:9) However, those who participate with her in her abominations, refusing to repent, will be cast into great tribulation and will be separated from God for all eternity. To God this is no laughing matter and it should not be to anyone who believes. "Let everyone who names the name of Christ depart from iniquity." (II Tim 2:19)