From O. Palmer Robertson’s The Christ of the Covenants (page 175, footnote 7):
The language of Meredith Kline is misleading on this point. His desire to maintain the distinctive emphasis of the law-covenant may be appreciated. But his statements too easily could be understood in a legalistic fashion. He interprets Paul as saying that the Sinaitic covenant “made inheritance to be by law, not by promise — not by faith, but by works” (By Oath Consigned, p. 23).
The distinctiveness of the Mosaic covenant resides in its externalized forms of law-administration. But the law under Moses cannot be understood as opening a new way of attaining salvation for God’s people. Israel must maintain the law, not in order to enter the favored condition of the covenant of redemption, but in order to continue in the blessings of the covenantal relationship after having been empowered to do so throught their covenantal oneness-with-God experienced by grace through faith alone. Under both the Mosaic and the Abrahamic covenants man experienced redemption by grace through faith in the work of the Christ who was to live and die in the place of sinners.
I must confess, I find the concept of earning an inheritance oxymoronic.