He Requires Heart-Obedience
The Jew relied upon the position given him by the privileges and rites of Judaism, although his religious life, as such, had shrunk within these outward things, as a seed rattles in its pod. The Apostle's argument is meant to show that personal irreligion and unbelief will neutralize all the benefit that outward rites might promise; while humble faith will compensate for any disadvantage which might result from heathen origin and environment.
The Jew will become as a Gentile, unless he have the spiritual counterpart to outward rites, while Gentiles will become as the Chosen People of God, if they have that separation of soul and life which was set forth in the initial rite of the Jew. See Colossians 2:11. The mere outward rite does not constitute sonship to Abraham; and he who has never undergone it, but by faith has put away all filthiness of flesh and spirit, is entitled to all the promises made to Abraham and his seed.