The doctrine of Galatians that those who preach a false gospel is clear, but we should not overlook the fact that Paul wrote to those who had been "bewitched" with a false gospel as if they were still brothers, because of his confidence that they could we restored, and did not hold firmly to a false gospel. The point being, not everyone who at some point in their lives expresses an incorrect formulation of the gospel is damned. Augustine's and Thomas's formulations of the gospel both exclude any imputation, and are somewhat similar, the main difference is that Thomas more clearly articulated what we call the doctrine of merit. Neither is orthodox from a protestant perspective, as Jacob has pointed out. Personally I do not feel the need to speculate on whether either is in heaven to read them. What errors they committed and how these errors can be avoided is the more pressing matter. Personally I would not recommend the reading of Thomas to those who cannot already explain reformed doctrine on all points from the Scriptures, and who have not already studied the biblical languages and our controversies with the church of Rome. Then one reads the fathers and scholastics to learn historical theology. This is the order that Hoornbeek recommends. But the Reformers give us a good example of how to usefully appropriate scholastic categories and learning, while rejecting their errors. It is unwise to try to start from zero, as if the reformation, or worse yet, old Princeton, or 20th century Westminster seminary, is the starting point and genesis of what is good and useful in theology. Our doctrine of God is in shambles and countless men who should know better have fallen into some form of Arianism or Tritheism in trying.