6 Moreover, you should know that in the old Scripture there lies the symbol of this Chrism. For what time Moses imparted to his brother the command of God, and made him High-priest, after bathing in water, he anointed him; and Aaron was called Christ or Anointed, evidently from the typical Chrism. So also the High-priest, in advancing Solomon to the kingdom, anointed him after he had bathed in Gihon. To them however these things happened in a figure, but to you not in a figure, but in truth; because you were truly anointed by the Holy Ghost. Christ is the beginning of your salvation; for He is truly the First-fruit, and you the mass; but if the First-fruit be holy, it is manifest that Its holiness will pass to the mass also.
Source: Catechetical Lectures (New Advent)