I think it is explained well in the first chapter of Isaiah. The Hebrews were making sacrifices to the Lord at that time to copy the heathens who made sacrifices as part of idol worship, not for forgiveness of sin. They were to make sacrifices of animals in the spirit of Christ, for the forgiveness of sins. Leviticus 4: 35 They shall remove all the fat, just as the fat is removed from the lamb of the fellowship offering, and the priest shall burn it on the altar on top of the food offerings presented to the Lord. In this way the priest will make atonement for them for the sin they have committed, and they will be forgiven.
Each physical, fleshly thing the Hebrews were told to do was to be an expression of a spiritual meaning. When the physical act was done and the spiritual meaning was ignored, the Lord said he hated the physical act.
God gave instructions to the Hebrews because they were the ones chosen to show
God to the world, but every instruction to them was for man, all of them, to be included when they accepted the Lord. In old testament time, no one accepted God who didn’t become a Hebrew. But as in all of the instructions God gives, it was for mankind, not Jews only. I think it is still true that every instruction the Lord gives us is still for mankind, never Jews only. I think our instructions about Judaizing is not about being against Jewish customs for God is only against sin, it is against only fleshly worship.
God opposes Judaizing because it is idolatry.
God means for the focus to be on Jesus and not on his shadow.
He is the substance, or the reality, that ceremonial elements of the Mosaic Law pointed toward.
That is one reason why the Temple was destroyed in AD70. It was a barrier to faith for Jews.
Now, Jews have substituted repentance and prayers for Temple worship, but they are no substitute. No righteousness can be gained by their repentance and prayers, outside of Christ.
I imagine by the original poster's history that the intention is to convince others they need to follow the calendar and dietary aspects of the Mosaic Law. These observances, too, were shadows and types (Colossians 2:16-17).
While it wouldn't be wrong for a Messianic Jew to observe them (or anyone else that wants to observe them in a non-judgmental way), it would be wrong if the intention is to force Christians to observe them, and to proclaim their observances to be pagan. That's the typical direction these sorts of conversations go.
I was raised in a family that believed the true faith involved observing the Sabbath and festivals, and the unclean meat laws. So, I know the mentality. But, realize that their observances are, at best, haphazard and not biblically faithful. For instance, some of them live in comfortable hotel rooms during the Feast of Tabernacles instead of shelters made of native Palestinian materials. Additionally, they don't observe them in the place God chose, Jerusalem (Deuteronomy 16:16).
They can't because there's no priest or other person to tell them God's will...nor can they provide the sacrifices required on these days since there's no Levitical priesthood.
Consistency isn't in their thoughts though
That's one of the things that unchained me from their belief system..I saw how remarkably inconsistent they were. Their system is basically just a patchwork quilt meant to cover their spiritual nakedness. I recommend being clothed in Jesus
