So, clearly, Jesus does use sinners to represent him. But what does this say about the trustworthiness of the teachings of those representatives (i.e., infallibility)?
We have already seen in Matthew 10:7 that Jesus appointed Judas to preach. But how could he know Judas, a thief and future traitor, would get it right? The answer lies further on in the same passage: “[W]hat you are to say will be given to you . . . for it is not you who speak, but the Spirit of your Father speaking through you” (Mt 10:19-20).
You see, Jesus wasn’t concerned about Judas misrepresenting the truth that he was sent out to teach because the Holy Spirit would guide him. Jesus made similar promises to all of the apostles at the Last Supper: “[The Father] will give you another Counselor, to be with you for ever . . . the Holy Spirit, whom the Father will send in my name, he will teach you all things, and bring to your remembrance all that I have said to you. . . . He will guide you into all the truth” (Jn 14:16, 26; 16:13).
And finally, Jesus’ promises are for all of his authoritative teachers until he returns in glory: “I am with you always, to the close of the age” (Mt 28:20).
The Christian faith “was once for all delivered to the saints” (Jude 1:3), and it has been authentically handed down and taught authoritatively by sinners—the apostles and their successors, the magisterium of the Catholic Church—under the guidance of the Holy Spirit for nearly two thousand years.
Thank God we do not have to rely on the personal holiness of Christ’s appointed representatives to know that what they are teaching is true.