This is a very profound principle, which is of immense value in dealing with Scripture. There were certain precepts and commands given to Israel, which are not of lasting obligation, because they were stages in their moral discipline and education. It would have been impossible to lift them suddenly from the degradation into which they had sunk in Egypt, to the glorious levels of Isaiah or the Sermon on the Mount: so God's dealings with them were graduated and progressive.
Such were the regulations about a plurality of wives, the keeping of bond-slaves, the treatment of captives, the destruction of their foes. With respect to these, our Lord says, Moses interposed a parenthesis of legislation, which was a stage higher than anything known among the surrounding nations, though it was not God's normal or original code.
What was true of Israel is true of us. We do not realize, in the first stage of our redemption, all that is included in the word "Sin." We are like men enveloped in morning mist, which permits them to descry only the bolder outlines of the cliffs around them, but as yet veils the minuter eminences or depressions. As the mist clears, surrounding objects become ever more distinctly defined: so that we know more of God, we know ourselves better, and realize what sin is, and come to see it where we had never guessed its presence. Thus we condemn to-day what we permitted five years ago. It is interesting to find in these words of Christ the germ of an argument which His apostle used afterward in the Epistle to the Galatians with such marvellous force. He said the Mosaic dispensation was a parenthesis; but it cannot disannul God's primal institution (Gal 3:15-17).