When God's righteousness is mentioned in the gospel, it is God's action of declaring righteous the unrighteous sinner who has faith in Jesus Christ. The righteousness by which a person is justified (declared righteous) is not his own but that of another, Christ.
Martin LutherTrue faith will no more fail to produce [good works] than the sun can cease to give light.
Martin LutherI frankly confess that even if it were possible I should not wish to have free choice given to me, or to have anything left in my own hands by which I might strive for salvation.
Martin LutherThe Bible is alive, it speaks to me; it has feet, it runs after me; it has hands, it lays hold of me.
Martin LutherWhen Satan tells me I am a sinner he comforts me immeasurably, since Christ died for sinners.
Martin Luther[Christ's] mission and work it is to help against sin and death, to justify and bring life. He has placed his help in baptism and the Sacrament [i.e., communion/Eucharist/Lord's supper], and incorporated it in the Word and preaching. To our eyes Baptism [capitalized in original] appears to be nothing more than ordinary water, and the Sacrament of Christ's body and blood simple bread and wine, like other bread and wine, and the sermon, hot air from a man's mouth. But we must not trust what our eyes see.
Martin Luther