Laudator Temporis Acti

Plutarch, Life of Aemilius Paulus 3.4-5 (on the office of augur; tr. Bernadotte Perrin):

For all the duties of this office were performed by him with skill and care, and he laid aside all other concerns when he was engaged in these, omitting nothing and adding nothing new, but ever contending even with his colleagues about the small details of ceremony, and explaining to them that, although the Deity was held to be good-natured and slow to censure acts of negligence, still, for the city at least it was a grievous thing to overlook and condone them; for no man begins at once with a great deed of lawlessness to disturb the civil polity, but those who remit their strictness in small matters break down also the guard that has been set over greater matters.

On not subtracting or adding (παραλείποντος οὐδὲν οὐδὲ καινοτομοῦντος), cf. Deuteronomy 4.2:

Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the LORD your God which I command you.

On strictness in small matters (τὴν ἐν τοῖς μικροῖς ἀκρίβειαν), cf. Luke 16.10:

He that is faithful in that which is least is faithful also in much: and he that is unjust in the least is unjust also in much.

Mary Beard et al., Religions of Rome, vol. I (Cambridge: Cambridge University Press, 1998), p. 52 (footnote omitted):

Roman religion placed a great deal of emphasis on the most meticulous repetition of the correct formulae; supposedly, the slightest error in performance, even a single wrong word, led to the repetition of the whole ritual.

On such repetition (instauratio) of a ceremony because of a defect in previous performance, see Plutarch, Life of Coriolanus 25.3 (tr. Bernadotte Perrin):

And it is customary for the Romans to renew sacrifices and processions and spectacles, not only for such a reason as the above, but also for trivial reasons. For instance, if one of the horses drawing the sacred chariots called Tensae gives out; or again, if the charioteer takes hold of the reins with his left hand, they decree that the procession be renewed. And in later ages, a single sacrifice has been performed thirty times, because again and again some failure or offence was thought to occur. Such is the reverent care of the Romans in religious matters.