In A New Testament Biblical Theology: The Unfolding of the Old Testament in the New, G.K. Beale asks, “How can believers be said to be judged by works and yet be justified by faith?” (e.g., Rom 2:13; Js 2:14-26; cf. Rom 3:28)

In the process of answering his question concerning what Beale tactfully calls this “consummate, manifestive stage of justification” (i.e., the justification according to works of which scripture speaks), Beale gives the following helpful illustration to help us understand this “twofold justification.”

A mundane illustration may help to clarify. In the United States, some large discount food stores require people to pay an annual fee to have the privilege of buying food at their store. Once this fee is paid, the member must present a card as evidence of having paid the fee. The card gets the members into the store, but it is not the ultimate reason that the person is granted access. The paid fee is the ultimate reason, the card being the evidence that the fee has been paid. We may refer to the paid fee as the “necessary causal condition” of store entrance and to the evidential card more simply as a “necessary condition.” The card is the external manifestation or proof that the price has been paid, so that both the money paid and the card issued are necessary for admittance, but they do not have the same conditional force for gaining entrance. We may call the paid fee a “first order” or “ultimate” condition and the card a “second order” condition.

He concludes,

Likewise, Christ’s justifying penal death is the price paid “once for all” (Heb. 9:12; cf. 9:26–28), and the good works done within the context of Christian faith become the inevitable evidence of such faith at the final judicial evaluation. Christ’s work is the “necessary causal condition” for justification, and the believer’s works are a “necessary condition” for it. Jonathan Edwards helpfully referred to Christ’s work as “causal justification” and the believer’s obedience at the end of the age as “manifestive justification.” This manifestive evidence not only is part of a judicial process but also becomes evidence that overturns the wrong verdict of the world on believers’ faith and works done in obedience to Christ.

G. K. Beale, A New Testament Biblical Theology: The Unfolding of the Old Testament in the New (Grand Rapids, MI: Baker Academic, 2011), 506–507.