Galatians 4:10

Ye observe days and months and seasons and years. I am afraid of you, lest by any means I have bestowed labor upon you in vain.

Sabbatarians have done their best to eliminate the meaning of this passage, but as Huxtable tells us, the words used here "were used by Josephus for the keeping of sabbath days";[17] and when read in conjunction with Colossians 2:16 there cannot be any doubt that the sin of the Galatians was simply that of keeping, after the Jewish manner, the sabbaths, festivals and special days of the Old Covenant, which if persisted in, would mean their total loss to Christianity. The whole thesis of this epistle is that "Judaism and Christianity do not mix."