2. It is necessary that we understand, first of all, the relation of the Old Testament as a whole to the system of revealed truth. It is a _preparatory_ revelation introductory to one that is _final_. This the New Testament teaches in explicit terms. "When the fulness of the time was come, God sent forth his Son." Gal. 4:4. Christ could not have come in the days of Enoch before the flood, nor of Abraham after the flood, because "the fulness of the time" had not yet arrived. Nor was the way for his advent prepared in the age of Moses, or David, or Isaiah, or Ezra. The gospel everywhere assumes that when the Saviour appeared, men had attained to a state of comparative maturity in respect to both the knowledge of God and the progress of human society. The attentive reader of the New Testament cannot fail to notice how fully its writers avail themselves of all the revelations which God had made in the Old Testament of himself, of the course of his providence, and of his purposes towards the human family. The _unity of God_, especially, is assumed as a truth so firmly established in the national faith of the Jews, that the doctrine of our Lord's deity, and that of the Holy Spirit, can be taught without the danger of its being misunderstood in a polytheistic sense--as if the Father, the Son, and the Holy Spirit were three gods. It is certain that this could not have been done any time before the Babylonish captivity. The idea of _vicarious sacrifice_, moreover--that great fundamental idea of the gospel that "without shedding of blood there is no remission"--the writers of the New Testament found ready at hand, and in its light they interpreted the mission of Christ. Upon his very first appearance, John the Baptist, his forerunner, exclaimed to the assembled multitudes: "Behold the Lamb of God, which taketh away the sin of the world." To the Jew, with his training under the Mosaic system of sacrifices, how significant were these words! Without such a previous training, how meaningless to him and to the world for which Christ died! Then again the gospel, in strong contrast with the Mosaic law, deals in _general principles_. Herein it assumes a comparative maturity of human thought--a capacity to include many particulars under one general idea. A beautiful illustration of this is our Lord's summary of social duties; "Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets." Matt. 7:12. We may add (what is indeed implied in the preceding remark) that the gospel required for its introduction a _well-developed state of civilization_ and culture, as contrasted with one of rude barbarism. Now the Hebrews were introduced, in the beginning of their national existence, to the civilization of Egypt; which, with all its defects, was perhaps as good a type as then existed in the world. Afterwards they were brought successively into