(These–and others–are some old notes that I had on Turretin which I thought I had published)
First of all, festivals properly so-called must be commanded by the divine word because God has the right of proscribing how he wants to be worshiped. The question then follows, do we see any such command? Any appeal to “unwritten tradition” assumes what it is trying to prove and thus commits the fallacy of “asserting the consequence” (It looks like this: if p, then q. Q; therefore, p. A Protestant inquirer could ask of the anchorites, “Where is the biblical warrant for practicing x? The anchorite could then respond, ‘St Paul told us to ‘hold to the traditions.’” The problem comes in the next question, “How do we know that the traditions that Paul mentioned are the ones you are doing today?” The anchorite can give one of two answers to this question: if he says that the the church has remained unbroken in its liturgy; therefore, it is the practices observed today, then he has just affirmed the consequent of his argument and reasoned fallaciously. On the other hand, he can admit that he doesn’t know if the traditions are the same, in which case the Reformed objection stands).
But what of Paul’s keeping the feast of Pentecost (Acts 20:16)? Several things may be observed: 1) This could be seen as the time-between-times of Old and New Covenant; 2) Paul nowhere intimates that it should be kept necessarily; 3) if it Pentecost is to be kept necessarily, in no way does it follow that saints’ days today are binding on the conscience.
An interesting Puritan take is seen in the following clip, where Generals Cromwell and Rainsborough force the surrender of some Cavaliers.