The question I raised at the end of my last post concerned how the monocovenantalism of the Federal Vision can affect how we think about the danger of, and remedy for, apostasy. (By "monocovenantalism" I mean the idea that man, from creation onward, has been in one continuous, gracious covenant with God.)
As an example of warning against apostasy, the epistle to the Hebrews cites the unfaithfulness of Old Testament Israel as a challenge to us today. In 3:12 - 4:11 we are exhorted not to fail to enter God's rest through sinful unbelief like the wilderness wanderers did, for though "the good news came to them, the message they heard did not benefit them" because of their unbelief (4:2).
What is crucial to understand is that the "rest" to which Israel aspired in Old Testament times was a type of the true, heavenly rest that Adam sought. And further, Israel's gaining or losing of that Sabbath rest, like Adam's, was contingent upon their obedience to God's law (Deut. 28:1-6).
Or to make my point more clear: Both the Adamic and Mosaic covenants were administered according to the legal principle, "Do this and live."
The antitype of Adam and Israel, of course, is Jesus Christ, the second Adam and faithful Israelite (Rom. 5:12ff; John 15:1ff). As the fulfillment of all the types and shadows of Old Testament times, he succeeded where his predesessors failed and faithfully earned the right to enter into his Father's Sabbath rest as our Champion and Forerunner.
While the danger of apostasy is still present and very real, the difference between our situation and that of Israel's is seen precisely at this point. Their "covenant faithfulness" was the basis for their enjoyment of Canaan, while our enjoyment of our heavenly homeland is the covenant faithfulness of Christ. Even the saving faith that we must exercise is provided for us as part of the "grace-by-faith" salvation that comes to us by virtue of the Abrahamic promise (Eph. 2:8-9).
The mistake of our Federal Vision brothers, it seems to me, is that they collapse two things that Paul keeps distinct, namely Israel's enjoyment of the earthly blessings of the Mosaic covenant, which was precarious and uncertain, and our enjoyment of the "spiritual blessings in the heavenly places" that Christ procured for us, which couldn't be more secure.