In Dr. R. C. Sproul’s latest book “Are We Together? A Protestant Analyzes Roman Catholicism” he outlines six core doctrines in which Roman Catholicism is at odds with the clear teaching of the Bible; namely her view of Scripture, the Church, the sacraments, the Papacy and the role of Mary. He also describes how Protestants should relate to Roman Catholics without minimizing the vital differences. I encourage you to read the foreword (by Dr. Michael Horton) as well as the introduction and sample chapter on justification:

The book is a clarion call to evangelicals to stand firm for the gospel, the precious good news of salvation by grace alone, through faith alone, in Christ alone, all to the glory of God alone. You can purchase it at the Ligonier store .