Patrick Fairbairn was a 19th-century minister in the Free Church of Scotland and Professor of Church History and Exegesis at Free Church College in Glasgow (now Trinity College). His most notable works included The Typology of Scripture, The Interpretation of Prophecy, and The Revelation of Law in Scripture. The following is an excerpt from his work An Exposition of Ezekiel (Evansville, IN: Sovereign Grace, 1960), which is especially relevant for current discussions on the question of republication in the Mosaic Covenant:
Neither Moses [Lev. 18:5] nor Ezekiel [20:11], it is obvious, meant that the life spoken of, which comprehends whatever is really excellent and good, was to be acquired by means of such conformity to the enactments of heaven; for life in that sense already was theirs [Israel’s], freely given and secured by the goodness of God in the covenant of promise. What they meant was, that only thus could the children of Israel retain possession of what was given, or attain to the secure and continued enjoyment of it. For as the statutes and ordinances, which God enjoined them to keep, were to constitute the outward form and expression of their spiritual being, so by the measure of their conformity to these must necessarily be determined what should belong to them, either of the goodness or of the blessedness of life. If life existed at all, this was the channel through which it was to flow, these were the signs and exhibitions which it was to give of itself. And just as in the natural sphere the exercise and discharge of all the appropriate functions is the way to sustain and invigorate, as well as to exhibit, the principle of life; so it might be said of Israel in respect to their covenant life, that by following the appointed channel of God’s institutions, it was to preserve itself in healthfulness and vigour. Doing these things, they lived in them; because life thus had its due exercise and nourishment and was in a condition to enjoy the manifold privileges and blessings secured in the covenant. And the very same may be said of the precepts and ordinances of the gospel: a man lives after the higher life of faith only in so far as he walks in conformity with these; for though he gets life through a simple act of faith in Christ, he cannot exercise, maintain and enjoy it but in connection with the institutions and requirements of the gospel. (pp. 215-16, emphasis original)
In other words, according to Fairbairn, the form of obedience may have differed between OT Israel and the NT church, but the same basic pattern or principle remains the same. For those who are first securely justified by grace through faith alone, law-keeping is the way of life and blessing. In this respect, law and gospel are not antithetical principles, but “sweetly comply” (Westminster Confession of Faith 19.7).