Romans 4:7 Blessed are those whose transgressions are forgiven, whose sins are covered.
The righteous man shall live by faith and not by law. This who are under faith, are not under the law. Their sins are covered, since the law does not apply to those twi live by faith. The difference between living by the law and living by faith is faith spontaneous and creative; living spirit. While law, composed of commandments contained in ordinance; law, is cast in stone; inanimate.
A good analogy for the difference between faith versus law, would be music. Someone under law in music, would do their best to reproduce a classic song in the exact way it was written; symphony orchestra. They seek perfection in the law of the song. The audience, who has heard the perfect song, will hear the slightest departures from the ideal song, which cause the musician to fall short of perfection; we all have sinned because we can't always be perfect.
When it comes to faith, faith is not cast into stone, like sheet music, rather it is a living spirit. In this case, the spirit may cause creative and spontaneous departure from the perfection of the original song written on sheet music. This is a covered sin, because the departure is being led by the spirit. It is not due to will power falling short, but it is due to following an inner hunch.
Sometimes a re-do, of an old song, becomes a new classic song. The original choice to remake of the old song; law, will be sinful because it lacks perfection defined by the original sheet music. However, it is covered sin, since the departure organically evolves a new song; lesson of life. The goals of the spirit trumps the law, just as life can assimilate inanimate matter to make it also alive.
Jesus made provisions for living by faith, which is called the forgiveness of sins. Say one was living by the spontaneous spirit of faith, and they got drunk one day. Even though drunkenness is defined as sin, this sin will be covered, since that day was inspired by the spirit. This who only know the perfection of the sheet music may not agree. Therefore if one starts to feels guilty, because of an inability to differentiate the spirit, from willful choice or just sloppiness, there is forgiveness of sins, until one learns to know the difference.
In the end, faith simplifies the law down to two things, love god and love your neighbor. Love god allows one to become open to the spirit of faith, while love your neighbor helps one not to judge others, since your neighbor may be of the spirit, too; covered sins?
Roman 8:15 The Spirit you received does not make you slaves, so that you live in fear again; rather, the Spirit you received brought about your adoption to sonship. And by him we cry, "Abba, Father."