The reason why this matters is because the plaintiffs in this lawsuit, known as Halbig v. Burwell, are hustling to try to convince the GOP-dominated Supreme Court to hear this case, where they no doubt believe that they have a greater chance of succeeding than in the DC Circuit, as a majority of the active judges in the DC Circuit are Democrats. The Supreme Court takes only a tiny fraction of the cases brought to their attention by parties who lost in a lower court — a study of the Court’s 2005 term, for example, found that the justices granted a full argument to only 78 of the 8,517 petitions seeking the high Court’s review that term. The justices, however, are particularly likely to hear cases where two federal appeals courts disagree about the same question of law.
Two hours after the divided DC Circuit panel released its opinion attempted to defund Obamacare, a unanimous panel of the Fourth Circuit upheld the health subsidies that are at issue in Halbig. Thus, so long as both decisions remained in effect, Supreme Court review was very likely. Now that the full DC Circuit has vacated the two Republican judges’ July judgement, Supreme Court review is much less likely.
In other words, if the full DC Circuit Court rules in favor of the government as expected, there's nothing that the Supreme Court needs to decide, and by choosing to not take the case up, the decisions will stand to allow the Affordable Care Act to work as intended.