I did not understand when I was a young believer in the Messiah that I was learning a theology, a man-made doctrine and belief system. Why do you think there are so many denominations? It is because they are not grounded in the doctrine of God's law. Proverbs 4:2 NKJV says, "For I give you good doctrine: Do not forsake my law."
It can be difficult to accept that we followed for the most part, doctrine that has been passed down to us from the pagan Roman Empire. Protestants say they are not Catholic but according to the Catholic Church, they are still Catholic because they keep the pagan sabbath. This was according to the Council of Constantinople in 360 AD.
The Roman Emperor Constantine was pagan, and he established the day of rest to the pagan sun god Mithras on Sunday. He worshipped the sun god Mithras probably along with all the pagan gods. He probably considered Yeshua to be just another pagan god. Sunday is the day of the pagan sun god.
From: https://sabbathfacts.org/constantine-sunday-law-321/
"The law stated that on 'the venerable day of the sun' all judges, city people, and craftsmen were to rest from their work. This meant that Christians who had previously observed the seventh-day Sabbath (Saturday) as a holy day now had to switch to Sunday."
The protestants are still keeping forms of the pagan religion that was passed down to them. Pagan Christianity also worships idols. No idol worshipper will be allowed in the kingdom of heaven (see Galatians 5:19-21). They changed God's commandments so they could worship idols. One of the 10 Commandments is very specific about not worshipping idols.
The Bible says in Exodus 20:4-6 NKJV,
You shall not make for yourself a carved image—any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; you shall not bow down to them nor serve them. For I, the LORD your God, am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generations of those who hate Me, but showing mercy to thousands, to those who love Me and keep My commandments.
Here are the Catholic 10 Commandments:
I, the Lord, am your God. You shall not have other gods besides me.
You shall not take the name of the Lord God in vain.
Remember to keep holy the Lord's Day.
Honor your father and your mother.
You shall not kill.
You shall not commit adultery.
You shall not steal.
You shall not bear false witness.
You shall not covet your neighbor's wife.
You shall not covet your neighbor's goods.
(From Learn Religions Online)
What happened to the commandment to not worship idols? Shaul said that idol worshippers will not be in God's future kingdom. They will say that through these idols we are really praying to God, but praying to these idols is idolatry. They believe a lie. 1 Corinthians 6:9-10 NKJV says, "Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God." According to the Bible, they are worshipping idols.