"Colossians 2:17b-18 Now of the body of Messiah, let no man deprive you, delighting in humble-mindedness and in worship of the messengers, intruding into the things he hath not seen, being vainly puffed up by the mind of his flesh,"(DLT: torahtimes.org).

the body: το δε σωμα. or sacrifice, or fellowship.  Paul probably means the corporate body here, the assembly or congregation of the faithful.  By fasting on the holy days, the ascetics cut themselves off from fellowship, but there is an intimation in Paul's usage of "body" here that they were also cutting themselves off from the benefits of Messiah.   The usual translation, "But the reality is Christ" is not a literal translation, and does not make the best sense in the context.   It is better to join the end of vs. 17 to the beginning of vs. 18, "the body" being the subject of the verb "deprive".   The ascetics also deprived those who joined them in their false worship of the fellowship of Messiah. (DLC: torahtimes.org)

Daniel's Literal Translation and Commentary: (http://www.torahtimes.org/translation/col0217.html)