In Mathew 5:17, Jesus said, "Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them, but to fulfill them.
What that means is the New Testament is not a new set of laws, with the old laws now taboo. Rather the NT is like an upgrade, into version 2.0. However, there will still be tech support for the older version 1.21.
The Old Testament law is like an operating system for human nature. When there is a Windows or IOS upgrade, more advanced featured are added to the newer version 2.0. However, the old system is not junked, but rather software support will still be provided for those who are more comfortable with the older system. It is OK to use either, but the NT is a more advanced version.
Paul distinguishes between these two operating systems. The new system was based on faith. All that is asked is to love God and love your neighbor. This is very open ended and very vague It requires faith in your inner voice and intuitive judgements. One may need to become creative and make unique judgements in unique situations where there is no law. The old system was based on laws, rules and procedures, which does not require faith, allowing even a nonbeliever to follow the rules, and be righteous.
Within Christianity, both versions are allowable, depending on whether one is a child of the promise; NT, or a child of the bondwoman; OT. The children of the promise are like sons and daughters of God, which means you are given a lot of slack, as you learn the charisma of faith.
Romans 4:7 "Blessed are those whose transgressions are forgiven, whose sins are covered.
The children of the bondwoman are more like the children of a servant, who have the ten commandments plus additional laws and rules to follow as a servant.
Ironically, many atheists chose a path, that is loosely similar to the children of the promise. Many try to do good, but they do not believe and/or follow the old laws. Many will experiment and take more liberty when choosing paths for themselves. But they lack the charisma of faith and are therefore, like adopted sons and daughters; halfway house.