I believe people who have the Holy Spirit could understand God's message from just reading the New testament. Its simple that a small child can understand it.
People just like make the gospel more complicated.
The old testament testifies of God's faithfulness and His redemption plans, but without the Holy Spirit and understanding of the New testament, it is incomplete and covered with a veil that makes it so people can't see the promises of Christ woven throughout the old testament.
I should add that I do not support "hyper grace". The hyper-grace folks do seem to be on fire for Jesus, but personally I am okay with plain ordinary wonderful godly grace. Mine doesn't have to be hyper as long as it's from God.
I also believe that grace gives us a saving faith in Jesus redeeming work on the cross unto salvation which justifies us...
However sanctification is a lifelong process and faith is but the first step.
We are to add to our faith virtue, not our own but Christ for,there is a verse that says virtue went out of Jesus and healed the woman afflicted with a bleeding issue for many years.
So we begin with faith, then are given the Holy spirit which is Christ's virtue or righteousness. Next He teaches us knowledge of what he expects of us and how to live a godly life. Then we move on to godliness, self control, perseverance, brotherly kindness and finally love.
Godliness and self control is something we need to strive for, however because we live in a fallen world we might stumble and fall back into sin. That is why we must learn perseverance and not stop just because the road is hard or we stumbled and fell into a pit.
We can recognise people who have walked with God the longest because of their brotherly kindness and love. It reflects God's peace and joy...I always think when meeting someone like that...I want to reflect God's manner in such a way that people will be able to see the joy, love and peace God has given me, instead of the worries, doubts and fears the world tries to burden me down with. I want to be like them and face the trials of this life and not despair but raise my eyes to Jesus and praise Him for increasing their patience.
So back to the title...the ten commandments were part of the old Covenant and shadows of reality in Jesus Christ.
The tabernacle in reality is the human flesh Jesus put on as a baby born of Mary. He did not have tablets of stone but the law written in His heart.
We have been promised the same. God will write His laws in our hearts.
There are two universal laws: love God with your whole heart, mind, body and life and love your neighbor as yourself.
Then there are other laws that are specific to individuals.
For example dietary laws....some people are allowed to eat meat and others with a weaker faith are commanded not to eat meat.
The same with the Sabbath and other Holy days....some people can worship God every day, others with a weaker faith need that weekly structure of routine and ritual to renew them and remind them of God's will in their life and His promise of rest.
Concerning such things people must obey God, not men.
Eat what God tells you can eat, worship as God commands you. However dont judge another man's servant, don't condemn others for not doing what YOU think they should but recognize that they might be doing exactly what God told them they should.