Don

Here is the way I would word it, gentiles are not capable of keeping the Noah covenant Torah and Israel is not capable of keeping the Mosaic covenant Torah by themselves.  ALL have sinned, ALL need Jesus.

Jesus perfectly kept the Mosaic covenant Torah, which is a superset of the Noah covenant Torah.  So both those not in the Mosaic covenant and those in it can be declared righteous in faith, not for following the rules of their covenants.  The REASON to follow the rules in any covenant is for the blessings of that covenant, but not to be saved by that covenant, as it is not the way to be saved, only faith in Messiah is the way to be saved.