John Calvin Commentary Numbers 18:1

"And Jehovah said unto Aaron, Thou and thy sons and thy fathers` house with thee shall bear the iniquity of the sanctuary; and thou and thy sons with thee shall bear the iniquity of your priesthood." — Numbers 18:1 (ASV)

And the Lord said to Aaron, You and your sons. By this solemn appeal, God stirs up the priests to devote themselves to their duty with the greatest fidelity and zeal. For He declares that if anything were done contrary to the requirements of religion, they would be accounted guilty of it, since those who are said to “bear the iniquity of the sanctuary” are the ones who sustain the crime and the punishment of all its pollutions.

God willed that the sanctuary be kept clear from every stain and defect, and also that the dignity of the priesthood be maintained in chastity and purity. A heavy burden, therefore, was imposed upon the priests when they were set over the holy things as their guardians, on the condition that if anything were done wrong, they were to be exposed to punishment, because the blame rested on them; just as if God had said that negligence alone was tantamount to sacrilege. Thus their honor, conjoined as it was with so much difficulty and danger, was by no means to be envied.

In this way God admonished them that the legal rites were of no trifling importance, since He so severely avenged all profanations of them. For from this it could easily be gathered that something far more excellent and altogether divine was to be sought in these earthly elements. This may also be very properly applied spiritually to all pastors, to whom blame is justly imputed if religion and the holiness of God’s worship are corrupted, if the purity of doctrine is impaired, or if the welfare of the people is endangered, since the care of all these things is entrusted to them.