For, on the one hand, there is a setting aside of a former commandment because of its weakness and uselessness (for the Law made nothing perfect), and on the other hand there is a bringing in of a better hope, through which we draw near to God. Hebrews 7:18-19The author of Hebrews (Paul, Apollos, Barnabas, Aquila, or Priscilla?) has been comparing the Old Testament covenant with the covenant instituted by the Lord Jesus Christ. This passage opened up a line of thought which I'd recommend you to consider:
We are not righteous of our own accord. In fact, all humanity is born with a tendency to sin. It's like coffee's natural inclination to get cold (and, therefore, nasty), our natural tendency is to drift from the perfection God has commanded. This has been our problem since Adam, Eve, and that whole fruit incident. That tendency has very diverse manifestation, but it's still ultimately the same: God is perfect, and we're not. It's like being born with a negative balance in our account.
Now, the Old Testament Law contains two major parts: 1.)Commands about living a holy life; 2.)Commands about sacrifices to cover failing to live a holy life. If you extract the narrative, that's Exodus, Leviticus, Numbers, and Deuteronomy. What I see is this: under the old way, man was expected to do his best, and offer sacrifices to bring him up to zero in his 'holiness account' before God. Now, further study of the OT shows that it was actually God's grace that accepted the sacrifices as adequate, but that's the essence of the Old Covenant. (Covenants are binding agreements. More in another post.)
The New Covenant works differently. As people, we're still born the same way we always have been, in debt to the holiness of God. We're still carrying a negative balance in our account. Except that when Jesus Christ, the Son of God, came and died as the substitute sacrifice for our sins, He changed the situation. Note that He didn't substitute for Old Testament sacrifices. He substituted for us. For those who have accepted Christ and surrendered to Him as Lord, His righteousness balances our account at zero. We are now capable of standing before God, because we have been credited with His account. Our lives are now about living in gratitude of that credit, and living up to it.
The Law, as the Hebrews passage points out, could not make us holy and perfect. It was structured to point out our lack of holiness and perfection, and to illuminate what has to be done about it. It is possible for us to be counted as perfect before God because of Christ, though we are now needing to live up to that credit we have received. Will we falter? Certainly, but we have no debt to work off any longer. We have only the gratitude we owe that brings us back, and keeps us in obedience to God.