So what's the difference, then?

To suggest, as too many do today, that the New Covenant differs from the Old by offering forgiveness in place of demanding obedience is a sad travesty. The New Covenant demands obedience every bit as strongly as does the Old one...So what is the difference between the two covenants? The difference is precisely where Jeremiah and Ezekiel place it. The Old Covenant was external. It stood over against the worshipper and, as such, it showed him or her in no uncertain terms who God was, and who he or she was...The New Covenant differs from the Old in this one respect. It is internal. Because of Christ’s sacrifice, the temple of our heart and spirit can be cleansed from the sins of the past and the Spirit can take up residence within us. Now God’s will can function from within us; now his nature can flow out of us. Now what was once an unattainable goal becomes a living reality. — Called to be Holy, pages 86-87

<idle musing>
Indeed! The difference is "Christ in you, the hope of glory." With Christ in us, there is no command of God we are unable to obey—but only through the power of the indwelling Christ via the Holy Spirit. That's quite a promise, isn't it?
</idle musing>