If we attempt to keep a set of do's and don'ts (the letter of the law), we will utterly fail (Galatians 6:13).
However, if we receive the Holy Spirit through faith in Christ (Galatians 3:14), and then walk according to that Spirit, the righteousness of the law will be fulfilled in us (Romans 8:4).
If we bear the fruit of the Spirit there is no law that will condemn us in our behaviour (Galatians 5:22-23). Therefore, we will be law-abiding citizens of the kingdom of heaven.
This is a righteousness apart from the law that is nevertheless attested to by the law and the prophets (Romans 3:21) that it is righteousness indeed.
The law reveals to us whether or not we are sinners (whether or not we are walkling according to the Spirit, so that the righteousness of the law is fulfilled in us). It shows us whether or not we are still sinners in need of a Saviour/ salvation.
For those who are born of God have it as their general disposition that they "do not" and "cannot sin.
Take that as hypoerbole if you like. For, if it is, then it is exaggeration to make a point.
What point? That if anyone is born again, their life will change and they will begin to walk in holiness and righteousness.
As it is written,
Pro 4:18, But the path of the just is as the shining light, that shineth more and more unto the perfect day.