Before you Gentiles knew God, you were slaves to so-called gods that do not even exist.
So now that you know God (or should I say, now that God knows you), why do you want to go back again and become slaves once more to the weak and useless spiritual principles of this world?
You are trying to earn favor with God by observing certain days or months or seasons or years.
I fear for you. Perhaps all my hard work with you was for nothing.