For Christ's People There Is No "What Lack I Yet?"

' The notion that the death of Christ is conditionally sufficient for all mankind, that is if all mankind were to believe in it, leads the sinner at once to the performance of some duty which he imagines will give efficacy to the death of Christ and render it available to him. By this means he is led to draw comfort from his duties instead of the finished salvation of Christ. This error is the fruitful cause of the disquieting fears and legal bondage of many professors. They are constantly in fear lest they have not performed the requisite condition and, after much toiling, their uneasy spirits are as far from rest as ever, and again they utter the old complaint, "What lack I yet?" They have no notion that the alone work of Christ made manifest to the heart by the Holy Spirit, is sufficient to give joy unspeakable without the performance of some duty on their part, and therefore they are in constant perplexity lest this important duty should not have been performed.
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In this state of bondage are many precious souls detained because they cannot see the absolute perfection of the work of Christ. They allow that Christ has done a great deal for sinners, but something they imagine must be done on our part to render his blood available; and that something not being able to satisfy divine justice and being too weak to purge their guilty conscience, they are disquieted. But when the soul is driven from every other refuge to trust in Christ alone then it finds rest. It no more asks, "What lack I yet?" knowing that the law is magnified, justice satisfied, and God the Father well pleased in his beloved Son: "for we who do believe have entered into rest." (Hebrews 4:3) "Comfort ye, comfort ye my people, saith your God. Speak ye comfortably to Jerusalem, and cry unto her, that her warfare is accomplished, that her iniquity is pardoned." (Isaiah 40:1-2) '

- excerpt from William Rushton's A Defense of Particular Redemption