Francis Beckwith has done a lot of good work. Though his reversion to Roman Catholicism is a mistake, I'm grateful for the good work he did as an Evangelical, and I'm glad that he did the right thing by resigning from the Evangelical Theological Society. Much of what needs to be said about Beckwith's reversion has already been said by people like James White, at his blog, and Douglas Groothuis and Jeff Downs, at Beckwith's blog. I would add the following. Francis Beckwith probably would agree with some of what I'm going to say, but it's sometimes worthwhile to state something that people have been assuming without stating. Making these things explicit might be helpful to some people who are looking on.
1. There can be a large degree of agreement with Roman Catholic theology among the church fathers without the conclusion following that we ought to consider the fathers Roman Catholic or that we ought to consider Catholicism true. On some issues, such as the veneration of images or some Marian doctrines, what Catholicism teaches was widely absent or contradicted among the earliest patristic sources. I would argue that the earliest Christians, including the earliest church fathers, held views on a large number of issues that are far from what Roman Catholicism believes (church government, prayer, the veneration of images, the afterlife, Mary, etc.). The earliest post-apostolic Christians repeatedly put forward a view of the afterlife that didn't include Purgatory, they didn't pray to the deceased and angels, infant baptism was initially absent and only gradually became popular, etc. It's true that justification through works is more prominent in patristic sources than justification through faith alone, for example, but such a vague similarity to Roman Catholicism doesn't make the fathers Catholic or Catholicism true. Similarly, it could be said that the fathers generally held a higher view of Mary than Evangelicals do, but a higher view of Mary isn't equivalent to a Roman Catholic view, and patristic views of Mary are closer to that of Evangelicalism the earlier we go.
2. Justification through works can be defined in more than one way, and there were many views of justification among the church fathers. See, for example, Tertullian's treatise On Baptism and Augustine's description of the large variety of views of justification in his day in The City Of God 21:17-27. It could be said that Mormonism and Roman Catholicism both believe in some form of justification through works, but it doesn't therefore follow that they hold the same view of justification. There are significant differences. Similarly, the patristic sources who advocate some form of justification through works disagree among themselves widely as to which works are required and which sins allegedly cause the loss of justification, for example. One of the earliest fathers, Hermas of Rome (note the significance of his location), for instance, believed in the concept of limited forgiveness (The Shepherd, 1:2:2). Roman bishops living shortly after the time of Hermas would oppose the concept, illustrating the diversity of views that could exist even in one city within a relatively short period of time. The patristic sources who advocate some form of justification through works differ widely in how they define the concept.
3. The Biblical evidence pertaining to justification is more significant than many people suggest. The Biblical documents were written over a span of more than a thousand years, and they address thousands of years of human history. The fact that the last book of the Bible was written in the first century A.D. doesn't mean that the Bible is just one first century source written by one author, which people might easily misunderstand. It's not as if we can go to somebody like Justin Martyr or Irenaeus and get the clarification we need regarding what the entire Bible meant when it was written several decades earlier. The church fathers were far removed from the original context of the Old Testament, and some of them were far removed from the original context of the New Testament. And if we think that we need clarification on something in Paul, for example, why wouldn't we go to somebody like Luke or John for that clarification before going to somebody like Hermas or Augustine? The concept of having the fathers clarify Biblical teaching on justification for us requires not only that one source needs clarification, but also that a long series of other sources needs clarification as well (the other Biblical authors). If you can read dozens of Biblical authors, yet still think that you need later sources to clarify major elements of the doctrine of justification for you (not minor details scripture doesn't address much), then the problem might be more with you than with an alleged lack of clarity in the Biblical documents.
4. Justification through faith alone is Biblical. It's doubtful that Paul would have placed so much emphasis on Genesis 15:6 if he meant to argue for some form of justification through works. All that Abraham does in that passage is believe (sola fide). That's not the sort of passage one chooses to illustrate justification through baptism, giving to the poor, or any other work. Jesus repeatedly forgives people as soon as they believe, prior to baptism or any other work (Mark 2:5, Luke 7:50, 17:19, 18:10-14), and that sort of justification at the time of faith is treated as normative elsewhere in the New Testament (Acts 15:7-11, 19:2, Galatians 3:2-9, Ephesians 1:13-14). Paul's question in Acts 19:2 assumes that it's normative to receive the Spirit at the time of faith, not at the time of baptism or at the time of anything else other than faith. Paul repeats that theme elsewhere, such as in Galatians 3:2-9. It would be implausible to dismiss all of these Biblical examples of sola fide as exceptions to a rule, especially given that some of the passages in question are explicitly in a normative context. Much more can be said for the Biblical case for a Protestant understanding of justification. In addition to the passages I've just cited, a Protestant view of justification makes more sense of other Biblical themes, such as the substitutionary nature of Christ's righteousness and atonement, the concept of looking to Christ and His work alone (1 Corinthians 2:2, Galatians 6:14), the freeness of eternal life, etc.
5. As some patristic scholars have noted, justification through faith alone is found in some sources during the patristic era. Protestants in general have noted this fact from the time of the reformers onward. Some, such as Philip Schaff, have thought that the concept is only rarely found in the fathers, while others, such as Thomas Oden, have argued that it's widespread. I think it's more common than Schaff suggests, but not as common as Oden has suggested. As with other issues, some of the patristic sources in question seem to have been inconsistent on the matter. But the concept of justification through faith alone is found in the patristic era. For some examples of where various Protestants see sola fide in the patristic sources, see D.H. Williams, Evangelicals And Tradition (Grand Rapids, Michigan: Baker Academic, 2005) and Bruce McCormack, Justification In Perspective (Grand Rapids, Michigan: Baker Academic, 2006). The common Roman Catholic claim that nobody advocated justification through faith alone between the time of the apostles and the Reformation is false. The concept is found in some church fathers and in some other sources who lived during the patristic era.
6. In his article linked at the beginning of this post, Beckwith tells us that he began his reading of the church fathers and other sources relevant to his reversion this past January. And this is May. He seems to have made too quick a judgment.
7. His appeals to "the church" have to be reconciled with the fact that there have been disagreements about how to define that term since patristic times. And even some sources who advocated a view of the church significantly different from what a Protestant would be willing to accept also differed from a Roman Catholic definition in some ways. Similarly, the concept of apostolic succession can be defined in multiple ways and has some significant problems as it's commonly used in modern Roman Catholic circles.