'Righteousness of God.' The absence of the article may arrest the mind here, and in some other places, in this part of the epistle. It is likely to do so, because the righteousness of God is now a known doctrine; not so when the apostle taught. The righteousness of God was a wholly new thought, as was indeed wrath from heaven: wrath on earth was not. The gospel, or 'glad tidings,' was the power of God to salvation, because righteousness of God (that kind of righteousness) was revealed -- not a righteousness required of man. See ch. 3.21.
'By faith.' The word 'by' is the same in Greek (ek) as that translated 'on the principle of.' I have left 'by' as being a quotation from Hab. 2.4.