For we know that the law is spiritual, but I am of the flesh, sold under sin.
Romans 7:14 ESV

This is the core of why the Hebrews were unable to allow the Law to be written on their hearts in Exodus. The death and resurrection of Yeshua enables the spirit to begin understanding and living out the Law, but ultimately the flesh also must die before it can be completely written on our hearts. See Deuteronomy 5:23-31 and Hebrews 8:7.

Obedience to the Law must begin in the spirit, not the flesh. Obedience in the flesh does nothing for your eternal state and often becomes just a burden, blinding you to spiritual truths and warping your understanding of the commandments. Obedience in the spirit begins to tame the passions of the flesh.