Couple quotes from Luther in the Lutheran Confessions :
That Jesus Christ, our God and Lord, died for our sins, and was raised again for our justification, Rom. 4:25.
And He alone is the Lamb of God which taketh away the sins of the world, John 1:29; and God has laid upon Him the iniquities of us all, Is. 53:6.
Likewise: All have sinned and are justified without merit [freely, and without their own works or merits] by His grace, through the redemption that is in Christ Jesus, in His blood, Rom. 3:23
I believe in the Lord Christ, God's Son, our Lord, dead, buried, and descended into hell. For in this [Confession] the burial and descent of Christ to hell are distinguished as different articles; and we simply believe that the entire person, God and man, after the burial descended into hell, conquered the devil, destroyed the power of hell, and took from the devil all his might. We should not, however, trouble ourselves with high and acute thoughts as to how this occurred; for with our reason and our five senses this article can be comprehended as little as the preceding one, how Christ is placed at the right hand of the almighty power and majesty of God; but we are simply to believe it and adhere to the Word [in such mysteries of faith]. Thus we retain the substance [sound doctrine] and [true] consolation that neither hell nor the devil can take captive or injure us and all who believe in Christhttp://www.bookofconcord.org/