He had once said, “I have yet many things to say unto you, but ye cannot hear them now;” but even then He added, “When He, the Spirit of truth, shall come, He will lead you into all truth.” He (thus) shows that there was nothing of which they were ignorant, to whom He had promised the future attainment of all truth by help of the Spirit of truth.
Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XXII