The Messiah and His Apostles taught directly out of the Tanakh (Old Testament) if we add or take away from the Law of our Heavenly Father, The Messiah's commandments, and the Law of Moses - we are defining a false prophet.
Deuteronomy 13:1–4 defines a false prophet:
If there arises among you a prophet or a dreamer of dreams, and he gives you a sign or a wonder,
and the sign or the wonder comes to pass, of which he spoke to you, saying, ‘Let us go after other gods’—which you have not known—‘and let us serve them,’
you shall not listen to the words of that prophet or that dreamer of dreams, for the LORD your God is testing you to know whether you love the LORD your God with all your heart and with all your soul.
You shall walk after the LORD your God and fear Him, and keep His commandments and obey His voice; you shall serve Him and hold fast to Him.
Elder Brother Peter warned about some of Elder Brother Paul's teachings being difficult to understand, leading the unstable astray 2 Peter 3:14-16:
Therefore, beloved, looking forward to these things, be diligent to be found by Him in peace, without spot and blameless;
and consider that the longsuffering of our Lord is salvation—as also our beloved brother Paul, according to the wisdom given to him, has written to you,
as also in all his epistles, speaking in them of these things, in which are some things hard to understand, which untaught and unstable people twist to their own destruction, as they do also the rest of the Scriptures.
Under the New Covenant (Jeremiah 31:31–34 / Hebrews 10) we find that:
Behold, the days are coming, says the LORD, when I will make a new covenant with the house of Israel and with the house of Judah—
not according to the covenant that I made with their fathers in the day that I took them by the hand to lead them out of the land of Egypt, My covenant which they broke, though I was a husband to them,[fn] says the LORD.
But this is the covenant that I will make with the house of Israel after those days, says the LORD: I will put My law in their minds, and write it on their hearts; and I will be their God, and they shall be My people.
No more shall every man teach his neighbor, and every man his brother, saying, ‘Know the LORD,’ for they all shall know Me, from the least of them to the greatest of them, says the LORD. For I will forgive their iniquity, and their sin I will remember no more.”
With true faith in Yehoshua the Messiah, we receive His Baptism of Fire and are blessed with His Holy Spirit. God then directly teaches us how to walk as the Messiah walked; blameless.
We will still sin until after judgment and the giving of our new Heavenly Bodies - and so there is an advocate with our Heavenly Father when we sin, that being Yehoshua the Messiah, the Righteous (He is the Spotless Animal sacrifice, the Bread, and Wine offering when looking at sacrifices and feast day offerings)
In Acts 15, for new Gentile Believers - avoid things given to idols, strangled meat, do not drink blood, and no sexual immorality. It then goes on to state Moses is taught every Seventh Day Sabbath (Friday Evening to Saturday Evening). A true believer, one who has received the true Holy Spirit of God Most High, will be led to learn and walk the rest of the Messiah's Commandments (the Law of Moses) as you grow in the faith. this includes the dietary law, feast days of Leviticus 23, new moon, etc.
Yehoshua the Messiah is boundless in Love and Mercy. He is the Perfect Teacher, He is the Good Shepherd, the Prophet, and Apostle. We are not saved by the Law, but because we love God, we learn and follow His Commandments.
The World does not recognize God or His ways, and so His ways seem strange, archaic, and restrictive. But for Yisra 'el, a true child of God Most High, it is a blessing and honor to learn and follow our Heavenly Father's Ways.
God does not change: Malachi 3
In the beginning was the Word, and the Word was with God, and the Word was God: John 1
Yehoshua the Messiah is the Same yesterday, today, and forever: Hebrews 13
The Righteous: Deuteronomy 6
Live By Faith: Hebrews 11