He quite firmly believes not only that his own private reading of the shortened protestant canon of Scripture is the True Faith, but that it is also the only source of truth.
It is thus quite useless to remind him that the Scriptures were fixed by councils of the Orthodox Church, that the Church existed before the New Testament was fully composed (Acts is a book of history, not prophecy, after all), or that the short canon he uses is missing books because the German reformers erroneously decided to follow the Christ-denying Jews of the Council of Jamnia.
Unfortunately, it is also equally useless to quote the Holy Scriptures to him in defense of the Faith, because it is not the Scriptures he trusts, but his own reading of them.
Thus, though we may cite Acts 15 as the model of concilar government in the Church, he will prefer private interpretation to the decisions of Church councils. Though we may cite St. Peter speaking of becoming through grace "partakers of the divine nature," and Our Lord commenting on the Psalmist's words "I have said ye are gods", he will not accept the Orthodox doctrine of salvation as theosis because it does not agree with his own interpretation of the Scriptures. Though we may cite Our Lord's words "This is my body" and "This is my blood" he will not accept the Orthodox doctrine of the reality of the Eucharist as the very body and blood of Christ because his interpretation is deaf to the plain meaning of those words and hears only "do this in rememberance of me" (and worse, does not fully understand the strength of the original word amanesis).
Don't bother arguing with him unless your really think that there are others on the thread who will be edified by your arguments.