The Supreme Court may sit and render final judgment en banc or in divisions, as may be prescribed by rules of the Court not inconsistent with the provisions of this section. No decision shall become the judgment of the Court, however, except on the concurrence of at least three justices, and no law shall be declared unconstitutional under either the Constitution of Virginia or the Constitution of the United States except on the concurrence of at least a majority of all justices of the Supreme Court. If the justices composing any division differ as to the judgment to be rendered in any cause or if any justice of such division, within a time and in a manner to be fixed by the rules of the Court, shall certify that in his opinion any decision of such division of the Court is in conflict with a prior decision of the Court, or of one of the divisions thereof, the case shall be reheard and decided by the Court sitting en banc.