OfTheCircumcision refers to those believers who were still steeped in Judaism. Such did not understand the parables of Jesus referring to new wine and new cloth. Mat 9:16,17
Faith in Christ Jesus results in being born as a NewSpirit being. It is the creation of new cloth, new wine skin. The new cloth should not be mingled with old cloth. The new wine skin is for new wine. That `new wine` is the HolySpirit.
Paul makes a very serious point about AnotherGospel in Gal 1:8,9 where he is addressing the same people whom Jesus forbade from mingling old cloth with new and from putting new wine in old bottles Mat 9:17,18 and the same people to whom the entire book of Hebrews is addressed and summarized in Heb 10:26.