Galatians 5:4 You who are trying to be justified by the law have been alienated from Christ; you have fallen away from grace.
We each have a choice as to whether we follow the law God gave to the Israelites or whether we follow Christ.
If we say we will follow one or the other, then we need to stick with that decision and follow it as best we can.
The Jews chose to continue following the law and Paul said if they make that decision they have to follow every aspect of that law – which can be grievous.
Jesus gives us to choice to simply ask forgiveness, total forgiveness which will cover everything we have done and then to try and do things His way for God.