We say that it is a superstition to esteem one day more holy than another. or to think that to abstain from labor is something which, in itself, pleases God (Rom 14:5, 6; Col 2:16, 17). But, following what the Lord has commanded, we sanctify one of the seven days (Gen 2:3). We devote it entirely to ecclesiastical assemblies to hear the Word of God; yet, as we have said, there is with us not Judaistic ceremony or stupid superstition. This is why we have not chosen the Jewish Sabbath, Saturday, but Sunday, following the custom of the early church (1 Cor 16:2; Acts 20:7; Rev 1:10).
As for other festival days, we have removed them as much as possible from us, especially those which have been introduced through manifest idolatry. We have done this so as to correct the innumerable abuses which flowed from such, and to relieve the poverty of many. Nevertheless, because there are certain festivals devoted, since ancient times, to the celebration of certain mysteries concerning our redemption, we use Christian liberty, and submit all to edification, according to the different circumstances of pleas, times, and persons.
Theodore Beza, The Christian Faith, 5.41