“Sin shall not have dominion over you, for you are not under the law but under grace” (Rom.6:14).
Although the throne of God is the habitation of His law, that law which is death to sinners, yet it is a throne of grace. We “come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need” (Heb. 4:16). Note-we are to come to obtain mercy. Note also that the top of the ark of the testimony in which were the tables of the law was called the mercy-seat. The ark if the earthly tabernacle not only represented the throne where God’s law is enshrined, but it represented that throne as the throne of grace.
“Even so grace might reign through righteousness to eternal life through Jesus Christ our Lord” (Rom. 5:21). Christ’s life was given for us and to us on the cross. By being crucified with Him we live with Him. In His heart was the law, so that the heart of Christ was really the throne of God. Sinai and Calvary are not in opposition, but are united. Both present the same gospel and the same law. The life which flows for us from Calvary bears to us the righteousness of the law that was produced from Sinai.
Thus we see how grace reigns through righteousness unto eternal life. Eternal life is in Christ, because His life is the life of the self-existent God who is from “everlasting to everlasting.” But the life of God is the law. The grace of God flows to us through the life of Christ, and thus in Christ we receive the law as it was ordained to life.
To accept the unspeakable gift of God grace therefore is simply to yield ourselves to Him, that Christ may dwell in us and live in us the righteousness of the law as spoken from Sinai, and treasured in the throne of God. From Christ that living stream still flows, so that receiving Him, we shall have in us that well of water spring up unto everlasting life.
Waggoner, Waggoner on Romans, pp. 105-108