I'm going by what Sproul said in his published books, rather than by someone's fallible memory of a lecture.
"In fact, only two or three books that were not included ever had real consideration. These were 1 Clement, The Shepherd of Hermas, and The Didache. These books were not included in the canon of Scripture because they were not written by apostles, and the writers themselves acknowledged that their authority was subordinate to the apostles." -- R. C. Sproul, Essential Truths of the Christian Faith, page 22.
Sproul is, of course, correct here. The New Testament books we have are either by apostles or by people closely associated with apostles, like Luke/Paul or Mark/Peter.