Galatians 2:14
But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, LIVEST AFTER THE MANNER OF GENTILES, and not as do the Jews, WHY COMPELLEST THOU THE GENTILES TO LIVE AS DO THE JEWS?

 A Jew is saying that by the way!

Galatians 4:8-11
 Howbeit then, when ye knew not God, ye did service unto them which by nature are no gods.  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.

Colossians 2:16-17
LET NO MAN  therefore JUDGE YOU in MEAT, or in DRINK, or in respect of an HOLYDAY, or of the NEW MOON, or of the SABBATH [days]:
Which are a shadow of things to come; but the body [is] of Christ.

This is saying let no man rebuke you in these matters.  Telling people they need to return to these things is casting judgment on them.  If you want to do it then go ahead, but don't make others feel as if they are not behaving themselves as proper Christians if they don't.  Paul called these thing WEAK AND BEGGARLY ELEMENTS.