Celebrating Christmas and Easter is wrong, Israel Folau told parishioners at his church last month.
So too is wetting babies' heads during Christenings.
For some time, the Wallabies superstar has been preaching during Sunday worship.
Folau, once purely a devout follower, has in the past 18 months developed into a church leader with strong opinions on Christianity.
He repeatedly attacks the Catholic Church and Christians who do not devoutly read the bible.
Giving the most comprehensive insight into Folau's mindset and beliefs, a video obtained by The Daily Telegraph shows one of the world's most famous rugby players attacking the "man-made" traditions of the two holiest periods in the Christian calendar.
"Christmas and Easter, that's man-made," Folau tells worshippers.
"For so many years we were caught up in the world thinking that celebrating Christmas was biblical, but when you read this passage you can see what God says about it."
Folau then reads Jeremiah 10: 1-5: "Hear ye the word which the Lord speaketh unto you, O house of Israel. Thus saith the Lord, learn not the way of the heathen, and be not dismayed at the signs of heaven; for the heathen are dismayed at them.
"For the customs of the people are vain: for one cutteth a tree out of the forest, the work of the hands of the workman, with the axe. They deck it with silver and with gold; they fasten it with nails and with hammers, that it move not.
"They are upright as the palm tree, but speak not: they must needs be borne, because they cannot go. Be not afraid of them; for they cannot do evil, neither also is it in them to do good."
Folau then looks to his listeners and says: "When you read that passage, you can already see it's talking about the Christmas tree.
"God is clearly saying, 'Do not follow the way of the heathen', which is what He's speaking of these people here, the custom, these people do it in vain.
"There's no point to doing it.
"If we don't go back to the scriptures and see what God says, we can easily fall into the tradition of man, thinking we're doing the right thing.
"There's a whole lot of people that go to church, but they're not following the doctrine of Christ.
"The problem with a lot of people today is they don't read the word, they go to church on Sunday, listen to what the pastor says, and that's it. They don't go back home to check for what the word of God says."
Folau also says: "The Catholic Church baptise babies with a sprinkling of water over the top of their head, things like that, that aren't even biblical."
Even Jesus' mother Mary comes in for criticism, as being held up by the church as an idol.
"What does the Catholic Church do? They create an image of Mary and Jesus and totally go against what God's word is. This is what I'm talking about, the difference between man's doctrine and tradition verses God's word," he says.
"We as people put something up in front of him to worship.
"What are we putting up in front of God that are idols? In this example I'm talking about Mary, but it could be things like money, or jobs, it could be things like our husbands or wives."
Israel Folau's contract is set to be terminated by Rugby Australia.
Rugby Australia CEO Raelene Castle confirmed the move last night, saying that unless the organisation receive "compelling mitigating factors", they plan to sack Folau, having received no response from the Waratahs star after he posted anti-gay comments on social media last night.
Folau has a history of making controversial, homophobic comments and his latest effort called on "drunks, homosexuals, adulterers, liars, fornicators, thieves, atheists and idolaters" to repent for their sins or else "hell awaits" them.
Major Wallabies sponsor Qantas, who threatened to pull its sponsorship last year following a series of provocative posts from Folau, hit out over the post, calling it "really disappointing" and Rugby Australia confirmed they intend to terminate his contract.
Having already outraged the gay community and large sections of the general public with his extreme views, this latest revelation is set to alienate Folau from many Catholic supporters who have come to his defence.