Before you Gentiles knew God, you were slaves to so-called gods that do not even exist.
And now that you have found God (or should I say, now that God has found you), why do you want to go back again and become slaves once more to the weak and useless spiritual powers of this world?
You are trying to find favor with God by what you do or don't do on certain days or months or seasons or years.
I fear for you. I am afraid that all my hard work for you was worth nothing.