Adherents say that God the Father resolves this problem by sending Christ, who is sinless and indestructibly perfect in character, to lead a perfect life and sacrifice himself for the sins of mankind. The sins of the repentant sinner are cast onto Christ, who is a perfect sacrifice. First of all, they note that the New Testament describes the method of man's salvation as the "righteousness of God" (Rom. 3:21, 22; 10:3; Philippians 3:9). They then note that this imputed righteousness is particularly that of Jesus Christ (2 Corinthians 5:21; 1 Corinthians 1:30). When they refer to the "imputed righteousness of Christ," they are referring to his intrinsic character as well as his life of sinlessness and perfect obedience to God's law on Earth, usually called his active obedience. The need for a human life of perfect obedience to God's law was the reason that Christ, who is God, had to become incarnate (take on human flesh) and live as a human being. Paul's statement in Romans 4:6, that God "imputes righteousness apart from works," is the basis for the fourth step in the argument that this righteousness of Christ is imputed to the believer's account. By this terminology, they mean that God legally credits the believer with the righteous acts that Christ performed while on this earth. Luther uses the language of a "fortunate exchange" to describe this concept, borrowed from St Paul's imagery in Colossians 3. Christ trades his "garments," holiness, righteousness, being blessed by God the Father, in exchange for human sin. This is really good news for sinners - Christ takes their sin and believers receive His blessed condition and righteousness.