believed: i.e. believed Jehovah = believed what he "heard" (Rom_10:17).
counted = reckoned or imputed. righteousness. No art. = as righteousness. This was positive imputed righteousness (because he believed concerning Christ). It was more than forensic righteousness, which was negative or nonimputation of sin (Psa_32:1, Psa_32:2). This was the consequence of the Gospel preached to Abram. (Compare Gal_3:8, and read Rom 4and Gal 3).