9 The purpose which sacred orators should keep before their mind in performing their duty may be understood from the fact that they may and ought to say of themselves, as did St. Paul "For Christ therefore we are ambassadors." [II Cor . v:20] If then they are ambassadors of Christ they ought to have the same purpose in discharging their office that Christ had in conferring it on them, nay, the very one that Christ Himself had while living upon earth. For neither the Apostles, nor the preachers who followed the Apostles had a different mission from Christ's: "As the Father hath sent me, I also send you." ( John xx:21] Now we know why Christ descended from heaven, for He says expressly: "For this came I into the world; that I should give testimony to the truth." ( John xviii:37] "I am come that they may have life." ( John x:10]
Source: Humani Generis Redemptionem (Vatican.va)