The Necessity of Christ's Priesthood

Crucial to understand the necessity of Christ's office as High Priest, is the relationship between God's mercy and His justice. Both of these are essential properties of God and His holiness. 

One might object that if both are essential properties, justice should give place to mercy. This rests upon the presupposition that one of these attributes must give place to the other. Owen responds:

"(1.) We shall make it fully appear that God hath, in infinite wisdom and grace, so ordered all things in this matter that no disadvantage doth redound either to his justice or his mercy, but that both of them are gloriously exercised, manifested, and exerted. That this was done by the substitution of the Son of God in their stead, to answer divine justice, who were to be pardoned by mercy, and that it could be done no otherwise, is that which we are in the confirmation of. And those by whom this is denied can give no tolerable account why all are not condemned, seeing God is infinitely righteous, or all are not pardoned, seeing he is infinitely merciful. For what they fancy concerning impenitency will not relieve them; for if God can forgive sin without any satisfaction unto his justice, he may forgive every sin, and will do so, because he is infinitely merciful; for what should hinder or stand in the way, if justice do not? But,— 

(2.) There is not the same reason of the actual exercise of justice and mercy; for upon the entrance of sin, as it respects the rule of God, the first thing that respects it is justice, whose part it is to preserve all things in their dependence on God; which without the punishment of sin cannot be done. But God is not obliged unto the exercise of mercy, nor doth the forbearance of such an exercise any way intrench upon the holiness of his nature or the glory of his rule. It is true, mercy is no less an essential property of God than justice; but neither the law, nor the state and order of things wherein they were created, nor their dependence on God as the supreme governor of the whole creation, raises any natural respect or obligation between mercy and its object. God, therefore, can execute the punishment which his justice requireth without the least impeachment of his mercy; for no act of justice is contrary unto mercy. But absolutely to pardon where the interest of justice is to punish, is contrary to the nature of God. 

(3.) It is denied that sin and misery do constitute the proper object of mercy. It is required that every thing contrary to the nature of God in sin and the sinner be taken out of the way, or there is no proper object for mercy. Such is the guilt of sin unsatisfied for. And moreover, faith and repentance are required to the same purpose. Socinus himself acknowledged that it is contrary to the nature of God to pardon impenitent sinners. These [faith and repentance] none can have but on the account of an antecedent reconciliation, as is evident in the fallen angels. And on these suppositions even mercy itself will be justly exercised, nor can it be otherwise." (John Owen)

It should be noted that the justice and mercy of God are not merely external effects of His will and power (though they are that), but are also essential properties of the nature of God. In neither way are they contradictory to one another:

"For in themselves, being essential properties of the nature of God, as they must be, in that they are perfections of an intelligent Being, they differ not from the universal rectitude of his holy nature, but only add a various respect unto external things; so that in themselves they are so far from being opposite, as that God is denominated just from the exercising the perfections of his nature in a way of justice, and merciful from a like exercise in a way of mercy. Absolutely, therefore, and essentially they are the same. Neither are their effects contrary or opposite to each other, only they are diverse, or not of the same kind; nor are the effects of the one contrary unto the other. To punish, where punishment is deserved, is not contrary to mercy; but where punishment is not deserved there it is so, for then it is cruelty. And yet also in that case, the part of wrong, namely, in punishing without desert, is more opposite to justice itself than the cruel part is to mercy. And so is it where punishment exceeds guilt, or where proceedings are not according unto an equal measure or standard. Nor is to spare through or by mercy contrary to justice; for if to spare and pardon be not for the good of the whole, for the preservation of order and the end of rule, it is not mercy to pardon or spare, but facility, remissness in government, or foolish pity" (John Owen)

A Few Arguments for the Necessity of Christ's Priesthood:

[1]. The Holiness of God Demands that Sin be Punished - (Genesis 18:25; Psalm 5:4-6; Habakkuk 1:13). Scripture sometimes expresses this as the jealousy of God (Exodus 20:5; Joshua 24:19).

[2]. God Hates Sin - (Numbers 25:4; Deuteronomy 13:17; Psalm 78:49; Romans 1:18)

[3]. With respect to sinners, God is called a consuming fire - (Deuteronomy 4:24; Hebrews 12:29)

[4]. If God did not exercise His justice in punishing sin, His glory would be violated (Proverbs 17:15)