While he speaks in a number of places of faith alone (unhyphenated) as the instrument by which we appropriate justification, he also insists that works must go with it, so closely related that justifying faith and works are almost identical…. This apparently means, despite his professed acceptance of the idea of faith alone as the way in which we receive justification, that in fact works are also involved. One cannot but conclude that works are part of faith, or that justification is attained by faith-works.
This raises various questions. When can one believe that he is justified? If works must go one as the absolute concomitant of faith, how long must the works be carried on before justification is achieved? This in turn raises the question of whether anyone can ever have any assurance of justification. One of Calvin’s repeated arguments against the Roman Church was that with its doctrine of faith plus works it left the believer in uncertainty as to his position before God. And as one looks at the history of the medieval church, one can see that this was the reason for the development of the doctrine of purgatory and indulgences, which really sparked the Reformation. In attempting to cover such charges against his views Shepherd declares that according to the WCF and the catechisms “good works are necessary for salvation.…that no less is necessary for maintenance of union and communion with Christ than was required for entrance into that union.” (p. 23) But this is very dubious in the light of other statements of the Westminster Standards and tends to erase the difference between justification and sanctification.
—W. Stanford Reid. Undated paper c. 1976–1979.