Albert Barnes on Galatians 6:15

For in Christ Jesus. In his religion. Gal 5:6.

But a new creature. The fact that a man is created anew, or born again constitutes the real difference between him and other men. This is what Christ requires; this is the distinction which he designs to make. It is not by conformity to certain rites and customs that a man is to be accepted; it is not by elevated rank, or by wealth, or beauty, or blood; it is not by the colour of the complexion; but the grand inquiry is, whether a man is born again, and is in fact a new creature in Christ Jesus. 2Cor 5:17, for an explanation of the phrase "a new creature."

(a) "For in Christ Jesus" Gal 5:6 (b) "new creature" 2Cor 5:17