Christ is the end of the law unto righteousness for everyone who believeth rom10:4
There are two covenants in the Sacred Scriptures. They are the individual covenant, which is seen in the OT expressed in circumcision, which made the individual and his family members of the nation of Israel, and the corporate covenant, which was seen in Yom Kippur (Lev 16) and made national Israel the people of God.
Unfortunately, in the Scriptures, it is often unclear as to which covenant is being spoken of, leading many people to conflate the principles of the individual covenant with the corporate covenant and vice versa.
Adam's sin broke the covenant relationship of mankind corporately. Because of this violation of the Law, all mankind, who were under the federal headship of Adam, were also affected by his disobedience. Now the question is whether Paul is speaking of individual response to God or corporate response to God.
Christ established a New Covenant and a new corporate congregation of God. Many of the verses which relate to our salvation have to do with Paul establishing that there is no keeping of the Law in the Old Covenant which could restore the severed relationship between God and man. Christ alone did that, restoring mankind to God.
But this does not have to do with our individual standing before God.
Sin is transgression of the law 1 John 3:4
The christian has a righteousness apart from the law Rom 3:21&22
The christian has no righteousness of observing the law/ works of the law Rom 3:20
Historically, the Jews were dependent upon their being Jewish and their observance of the Law. Christ's title as the "Last Adam" shows us that there were many other "Adams" who could have restored the corporate covenant and returned mankind to God. All failed, for all failed to keep the Law perfectly. That obedience was needed to restore mankind to God. Paul was dealing with those who refused to see that Christ is the end of the Law which kept mankind separated from God. Christ has kept the Law, mankind is reunited to God, there is no more of the Law as regards showing us our separation from God. The New Covenant, corporately speaking, is established in Christ.
But there is still the issue of each one of us coming to salvation. This means that we must make our own covenant with Christ and by doing so, become part of the congregation of God. This individual covenant has nothing to do with the Law of God. It is guided by the principles of a covenant under a new set of laws. The Old Covenant Law showed man his separation from God and gave the Law which needed to be kept in order to restore mankind.
The New Covenant Law is based on the principles which Christ Himself said when He said that the first and greatest Law is to love God with all our being and the second Law is to love one's neighbor as one's self.
If righteousness means "right standing with God," then yes, no man could be justified by keeping the Law, because unless the Law was kept perfectly, man and mankind still remained separated from God. Yet the Scriptures are filled with statements regarding people in the Old Covenant who were righteous. So which was it? Well, it was that they were indeed righteous as far as their individual relationship with God, but they did not keep the Law in a manner which was able to restore man to God.
The above is only possible I Jesus died for all a Christians sins at Calvary, past, present and future. Refute that from the texts given
There is no such thing as dying for future sins. This is a Protestant fantasy called "forensic justification" in which it is said that because of Christ's death, God makes a judicial declaration of "not guilty" in the courts of heaven, thus wiping the entire slate clean for the Christian. That violates the principle of oaths/sanctions which is one of the five principles of a covenant relationship.