Acts: About Justification

The entire book of Acts speaks of nothing else but that Jews as well as Gentiles, the righteous as well as the unrighteous, are justified only faith in Christ Jesus, without the Law and works. The sermons of the apostles, Peter, Paul, Stephen, Philip,and others show this, as well as the examples of the Gentiles and the Jews. For just as God by the preaching of the Gospel gave the Holy Ghost to the Genties, who lived without the Law, so He gave Him also to the Jews, not through the Law, not through the ceremonies and sacrifices prescribed in the Law, but through the preaching of faith alone. Now if the Law had been able to justify, and the righteousness of the Law had been necessary for salvation, then the Holy Ghost would certainly not have been given to the Gentiles, who had not kept the Law. 

Source: Quoted in Ewald M. Plass, What Luther Says, A Practical In-home Theology for the Active Christian.  St. Louis: Concordia Publishing House.  1959 Edition, 10th Printing (1994), p. 702.