In this life we cannot live up to the law, because our sinful nature does not stop bringing forth evil desires, even though the Spirit in us resists them.
But someone might ask: "Since we also grant that love is a work of the Holy Spirit, and since it is righteousness because it is the fulfillment of the law, why do we not teach that it justifies?" We must respond to this. In the first place, it is certain that we do not receive the forgiveness of sins either through our love or on account of our love, but on account of Christ, by faith alone. By focusing on the promise and thus realizing that faith alone conquers the terrors of sin and death, it is certainly firm that God pardons (because Christ did not die in vain). Whoever doubts the forgiveness of sins insults Christ by thinking that such sin is greater or stronger than the death and promise of Christ, even though Paul says [Rom.5:20] that "where sin increased, grace abounded all the more," that is, mercy is more plenteous than sin. Whoever thinks that receiving the forgiveness of sins is a result of acts of love insults Christ and will discover in the judgment of God that such faith in one's own righteousness is wicked and futile. Therefore, it must be that faith reconciles and makes a righteous person out of an unrighteous one. We do not receive the forgiveness of sins on account of love for God. (paragraphs 146-151)