When it comes to the new covenant, many people confuse the function of faith with the works of law. In the old testament when a man wanted to be righteous he had to obey the law to the letter. But through Abraham God reveals a righteousness that is not by the working of the law but rather by faith.
That's why the verses show us that Abraham was credited righteousness because he believed that he who had promised was faithful and able. This is why many Christians today can not obtain the righteousness which is by faith because they seek to do the works without trusting the one who promised.
That you feel your heart is at peace with God doesn't make you righteous; likewise, when your heart condemns you does not make you guilty of sin before God. But the understanding of the faith that is in God makes you a child of God.
Hallelujah. Amen