In many ethical maxim texts (including the “Delphic Maxims” and the Precepts of Apollon), the paired injunctions “honor the gods, honor your parents” appear at the beginning of the list. They are, even beyond maxim literature, often the starting points of Greco-Roman ethical thought. (And the same two rules, in different formulation, open the Greco-Egyptian logos of Euphantus.) In a work ascribed to the Athenian orator Isocrates (4th century BCE), they are at one point (To Demonicus 16) listed along with two other precepts, giving a kind of bedrock of norms.
This formulation was evidently popular, being included in two ancient anthologies (Orion and John Stobaeus) and quoted twice in later authors (see section 3 below and here). I translate it along with an ancient explanation, a fuller statement of the same ideas in Isocrates, and a similar passage from the tragedian Euripides (5th century BCE).
Note that these maxims are the beginning of ethical thought, not the be-all and end-all. For example, as several ancient writers point out, filial piety (respect for your parents) does not entail following or supporting them in unjust actions, since injustice is a dereliction of our moral obligation to the gods. Analogous qualifications hold concerning the commandment to follow the law.
2 Isocrates, To Demonicus 16
(1) Fear the gods (θεοὺς φοβοῦ),
(2) Honor your parents (γονεῖς τίμα),
(3) Respect your friends* (φίλους αἰσχύνου),
(4) Obey the laws (νόμοις πείθου).
[*Literally, ‘have a sense of shame before your friends’.]
3 Explanation of To Demonicus 16 in the anonymous commentary on Hermogenes’ Peri ideōn
“Fear the gods, honor your parents, respect your friends”: These sayings are arranged in a natural order, because the gods existed first, then the parents from whom we are born, and only after that do we become friends with others.
4 Fuller statement (Isocrates, To Demonicus 13–14)
First of all, do pious actions towards the gods, not only by sacrificing, but also by keeping your oaths, because the former is a sign of wealth in possessions, but the latter is an indication of moral goodness in your behavior. Always honor the divine (daimonion), but especially together with the state;* in that way, you will have the reputation of sacrificing to the gods and also of abiding by the laws.
Behave towards your parents as you would wish your own children to behave towards you.
[*I.e., in the same manner as is customary and at the occasions when there are public festivities.]
5 Quotation from Euripides (preserved in John Stobaeus, Anthology 3.1.80)
There are three virtues which you need to practice, child:
To honor the gods and the parents who reared you,
As well as the common laws of Greece; and if you do these things
You will always have the most noble crown of a good reputation.