He fulfilled the Sabbaths, and the Festivals, and the laws of sacrifice so that we don't need to do those anymore (but we can if we want). But the outstanding
debt of law that remains to be fulfilled through Christ in us is the law summed up in "love your neighbor as yourself".
Romans 13:8-10
8Let no debt remain outstanding, except the continuing debt to love one another, for whoever loves others has fulfilled the law. 9The commandments, “You shall not commit adultery,” “You shall not murder,” “You shall not steal,” “You shall not covet,”
a and whatever other command there may be, are summed up in this one command: “Love your neighbor as yourself.”
b 10Love does no harm to a neighbor. Therefore
love is the fulfillment of the law.
Christ did not fulfill the debt of love for others for us so that we don't have to do that. It will be fulfilled through Christ when you actually do it through your faith in Christ. If you don't do that, and can't do that, then you are not born again. Only born again people can fulfill the outstanding debt of law that remains for the people of God to literally fulfill through the power of the Spirit. Dead faith, which has been taught to the church for quite a while now as being saving faith, does not fulfill the remaining debt of the law to love others (don't slander, don't hate, and various other laws). It shows you to not be born again and so you will not be saved when Jesus comes back.