47 He is the good Physician, Who has taken upon Him our infirmities, has healed our sicknesses, and yet He, as it is written, honoured not Himself to be made a High Priest, but He Who spoke to Him. The Father said: “You are My Son, this day have I begotten You.” As He said in another place: “You are a Priest for ever after the order of Melchisedech.” Who, since He was the type of all future priests, took our flesh upon Him, that “in the days of His flesh He might offer prayers and supplications with a loud voice and tears; and by those things which He suffered, though He was the Son of God, might seem to learn obedience, which He taught us, that He might be made to us the Author of Salvation.” And at last when His sufferings were completed, as though completed and made perfect Himself, He gave health to all, He bore the sin of all.
Source: Letters (New Advent)