It was reckoned unto him for righteousness (ελογισθη εις δικαιοσυνην). First aorist passive indicative of λογιζομα, old and common verb to set down accounts (literally or metaphorically). It was set down on the credit side of the ledger "for" (εις as often) righteousness. What was set down? His believing God (επιστευσεν τω θεω).