Still a Valid Admonition for Today?

Wherefore it is incumbent to obey the presbyters who are in the Church—those who, as I have shown, possess the succession from the apostles; those who, together with the succession of the episcopate, have received the certain gift of truth, according to the good pleasure of the Father. But [it is also incumbent] to hold in suspicion others who depart from the primitive succession, and assemble themselves together in any place whatsoever, [looking upon them] either as heretics of perverse minds, or as schismatics puffed up and self-pleasing, or again as hypocrites, acting thus for the sake of lucre and vainglory. For all these have fallen from the truth. - St Irenaeus, Against Heresies, IV 26:2

Craftily Decked Out

Error, indeed, is never set forth in its naked deformity, lest, being thus exposed, it should at once be detected. But it is craftily decked out in an attractive dress, so as, by its outwardform, to make it appear to the inexperienced (ridiculous as the expression may seem) more true than the truth itself. - St. Irenaeus, Against Heresies, Preface

Mormonism comes to mind. Cleverly disguised reinterpretation.

Of Guessing at Things Above.

"It is very shameful, and not only shameful, but very foolish, to take from things below a guess at things above, and from a fluctuating nature at the things that are unchanging, and as Isaiah says, to seek the Living among the dead." - St. Gregrory Nazianzen, Fifth Theological Oration, X

The discontinuity of being. It serves as a reminder to be very careful in looking around about (and at myself) and by analogy or deduction arrive at an understanding of God.