This was a good book to deal with basic protestant objections. Rock and Sand is a good one, ladder of divine ascent is literally a classic, fr seraphim rose's book on life after death was decent. Heavier scholarly work such as the 7 eccumenical councils was written by a catholic but gives a great non bias overview of what was going on. Then you have the orthodox church by mcguckin which is a high level version of know the faith.