It is plain, then, that law-keeping did not figure at that juncture as the meritorious ground of life-inheritance. The latter is based on grace alone, no less emphatically than Paul himself places salvation on that ground. But, while this is so, it might still be objected, that law-observance, if not the ground for receiving, is yet made the ground for retention of the privileges inherited. Here it cannot, of course, be denied that a real connection exists. But the Judaizers went wrong in inferring that the connection must be meritorious, that, if Israel keeps the cherished gifts of Jehovah through the observance of His law, this must be so, because in strict justice they had earned them. The connection is of a totally different kind. It belongs not to the legal sphere of merit, but to the symbolico-typical sphere of appropriateness of expression.
—Geerhardus Vos, Biblical Theology, 127.