God gives the heavenly righteousness necessary to gain entrance into the kingdom of heaven to sinners who will pursue it; the proof of which is found in the ability to walk in it.
In our pursuit of righteous we are to humbly judge our own sin first, then helpfully judge our brother’s sin, so that together we display the righteousness of the kingdom through loving relationships.
Jesus is the fulfillment of the Old Testament, including the righteous standard of the Mosaic Covenant that we need in order to enter the kingdom of heaven.