Tertullian on the Vicar of Christ Around 207CE

Our Lord Christ has surnamed Himself Truth, not Custom. If Christ is always, and prior to all, equally truth is a thing everlasting and ancient. Let those therefore look to themselves, to whom that is new which is intrinsically old. It is not so much novelty as truth which convicts heresies. Whatever savors of opposition to truth, this will be heresy, even (if it be an) ancient custom. …

The rule of faith, indeed, is altogether one, alone immoveable and irreformable; the rule of believing in one only God omnipotent, the Creator of the universe, and His Son Jesus Christ, born of the Virgin Mary, crucified under Pontius Pilate, raised again the third day from the dead, received in the heavens, sitting now at the right (hand) of the Father, destined to come to judge quick and dead through the resurrection of the flesh as well (as of the spirit). …

For what kind of (supposition) is it, that, while the devil is always operating and adding daily to the ingenuities of iniquity, the work of God should either have ceased, or else have desisted from advancing? On the contrary, the reason why the Lord sent the Paraclete was that, since human mediocrity was unable to take in all things at once, discipline should, little by little, be directed and ordained and carried on to perfection by that Vicar of the Lord, the Holy Spirit. “Still,” He said, “I have many things to say to you, but you are not yet able to bear them: when that Spirit of truth shall come, He will direct you into all truth, and will report to you the things that must take place.”