Regarding it in the broadest way, and as a purely human institution, we may trace it back to the eternal conflict in the breast of man between two mighty tendencies—the thirst for God and the dread of Him, a strong instinct of approach and a repelling sense of unworthiness.
In every age and climate, man prays. If any curious inquirer into savage habits can point to the doubtful exception of a tribe seemingly without a ritual, he will not really show that religion is one with superstition; for they who are said to have escaped its grasp are never the most advanced and civilised among their fellows upon that account,—they are the most savage and debased, they are to humanity what the only people which has formally renounced God is fast becoming among the European races.
Certainly history cannot exhibit one community, progressive, energetic and civilised, which did not feel that more was needful and might be had than its own resources could supply, and stretch aloft to a Supreme Being the hands which were so deft to handle the weapon and the tool. Certainly all experience proves that the foundations of national greatness are laid in national piety, so that the practical result of worship, and of the belief that God responds, has not been to dull the energies of man, but to inspire him with the self-respect befitting a confidant of deity, and to brace him for labours worthy of one who draws, from the sense of Divine favour, the hope of an infinite advance.
And yet, side by side with this spiritual gravitation, there has always been recoil and dread, such as was expressed when Moses hid his face because he was afraid to look upon God.
Now, it is not this apprehension, taken alone, which proves man to be a fallen creature: it is the combination of the dread of God with the desire of Him. Why should we shrink from our supreme Good, except as a sick man turns away from his natural food? He is in an unnatural and morbid state of body, and we of soul.
Thus divided between fear and attraction, man has fallen upon the device of commissioning some one to represent him before God. The priest on earth has come by the same road with so many other mediators—angel and demigod, saint and virgin.
At first it has been the secular chief of the family, tribe or nation, who has seemed least unworthy to negotiate as well with heaven as with centres of interest upon earth. But by degrees the duty has everywhere been transferred into professional hands, patriarch and king recoiling, feeling the inconsistency of his earthly duties with these sacred ones, finding his hands to be too soiled and his heart too heavily weighted with sin for the tremendous Presence into which the family or the tribe would press him. And yet the union of the two functions might be the ideal; and the sigh of all truly enlightened hearts might be for a priest sitting upon his throne, a priest after the order of Melchizedek. But thus it came to pass that an official, a clique, perhaps a family, was chosen from among men in things pertaining to God, and the institution of the priesthood was perfected.
Now, this is the very process which is recognised in Scripture; for these two conflicting forces were altogether sound and right. Man ought to desire God, for Whom he was created, and Whose voice in the garden was once so welcome: but also he ought to shrink back from Him, afraid now, because he is conscious of his own nakedness, because he has eaten of the forbidden fruit.
Accordingly, as the nation is led out from Egypt, we find that its intercourse with heaven is at once real and indirect. The leader is virtually the priest as well, at whose intercession Amalek is vanquished and the sin of the golden calf is pardoned, who entered the presence of God and received the law upon their behalf, when they feared to hear His voice lest they should die, and by whose hand the blood of the covenant was sprinkled upon the people, when they had sworn to obey all that the Lord had said (xvii. 11, xxxii. 30, xx. 19, xxiv. 8).
Soon, however, the express command of God provided for an orthodox and edifying transfer of the priestly function from Moses to his brother Aaron. Some such division of duties between the secular chief and the religious priest would no doubt have come, in Israel as elsewhere, as soon as Moses disappeared; but it might have come after a very different fashion, associated with heresy and schism. Especially would it have been demanded why the family of Moses, if the chieftainship must pass away from it, could not retain the religious leadership. We know how cogent such a plea would have appeared; for, although the transfer was made publicly and by his own act, yet no sooner did the nation begin to split into tribal subdivisions, amid the confused efforts of each to conquer its own share of the inheritance, than we find the grandson of Moses securely establishing himself and his posterity in the apostate and semi-idolatrous worship of Shechem (Judg. xviii. 30, R.V.).