Though a pagan calendar is possible, the context of the letter as a whole suggests that the old covenant calendar is in view.1 The Galatian believers are giving themselves to keeping old covenant law. Special days would then be Sabbaths and other festival days (Colossians 2:16). Months would be new moon observances (Numbers 28:11–15). Seasons would be feasts that last more than one day (Leviticus 23:1–44) and years are either Sabbatical or Jubilee years, possibly also new year celebrations.2
10 You observe days and months and seasons and years!