Galatians 4:8-11

But at that time, when you did not know [the true] God and were unacquainted with Him, you [Gentiles] were slaves to those [pagan] things which by [their very] nature were not and could not be gods at all. Now, however, since you have come to know [the true] God [through personal experience], or rather to be known by God, how is it that you are turning back again to the weak and worthless elemental principles [of religions and philosophies], to which you want to be enslaved all over again? [For example,] you observe [particular] days and months and seasons and years. I fear for you, that perhaps I have labored [to the point of exhaustion] over you in vain.