Weak and beggarly elements: Observing days, and months, and times, and years

God's Word says,

"But now, after that ye have known God, or rather are known of God, how turn ye again to the weak and beggarly elements, whereunto ye desire again to be in bondage? Ye observe days, and months, and times, and years. I am afraid of you, lest I have bestowed upon you labour in vain." (Galatians 4:9-11)