Temperance.
Temperance and honoring the gods. It’s the best we can do.
The smartest thing mortals can choose to do.

[τὸ σωφρονεῖν δὲ καὶ σέβειν τὰ τῶν θεῶν
κάλλιστον: οἶμαι δ᾽ αὐτὸ καὶ σοφώτατον
θνητοῖσιν εἶναι κτῆμα τοῖσι χρωμένοις.]

Euripides (485?-406? BC) Greek tragic dramatist

Bacchæ [Βάκχαι], l. 1150ff [Messenger/Ἄγγελος] (405 BC) [tr. Pauly (2019)]
    (Source)

After recounting the brutal murder and dismemberment of Pentheus by the Bacchantes in punishment of his disrespect to Dionysus.

(Source (Greek)). Alternate translations:

For modest worth, and reverence for the Gods,
Are, in my judgement, the most certain marks
Of glory and of wisdom in mankind.
[tr. Wodhull (1809)]

Soundness of mind and reverence for the affairs of the gods is best; and this, I think, is the wisest possession for those mortals who adopt it.
[tr. Buckley (1850)]

Oh! to be reverent, to adore the gods,
This is the noblest, wisest course of man,
Taking dread warning from this dire event.
[tr. Milman (1865)]

For soberness and reverence for the gods
I deem the wisest and the best of things
To all such men as learn this lesson well.
[tr. Rogers (1872)]

To my mind self-restraint and reverence for the things of God point alike the best and wisest course for all mortals who pursue them.
[tr. Coleridge (1891)]

Ay, self-restraint, and reverence for the Gods
Are best, I ween; 'tis wisest far for men
To get these in possession, and cleave thereto.
[tr. Way (1898)]

Oh, to fulfil
God's laws, and have no thought beyond His will,
Is man's best treasure. Aye, and wisdom true,
Methinks, for things of dust to cleave unto!
[tr. Murray (1902)]

Humility,
a sense of reverence before the sons of heaven --
of all the prizes that a mortal man might win,
these, I say, are wisest; these are best.
[tr. Arrowsmith (1960)]

To be of sound mind and reverence the things divine
is finest -- and I think it is also the wisest
practice for mortal men to follow.
[tr. Kirk (1970)]

The noblest thing a man can have is a humble and quiet heart that reveres the gods. I think that is also the wisest thing for a man to possess, if he will be use it.
[tr. Vellacott (1973)]

Pure thought, and reverence for what is god’s --
this is the fairest and, I think, the wisest
possession mortals can employ.
[tr. Neuburg (1988)]

I am but a simple man, yet to me
reverence and humility before the Gods
is best for all men. It is also the only wisdom.
If only men would use it. So I think.
[tr. Cacoyannis (1982)]

To be moderate and honor godly things
Is best. I think it the wisest possession
For mortal men, if they use it well.
[tr. Blessington (1993)]

Moderation and reverence for things divine,
this is the best course. And it is also, I think,
the wisest possession for those mortals who use it.
[tr. Esposito (1998)]

But this is the highest glory: have a sound mind and reverence for
whatever belongs to the gods. This too is the most wise
of all pursuits a human being can follow.
[tr. Woodruff (1999)]

Wise moderation and a reverence
For what is of the gods -- this is what’s best.
And this, I think, of all possessions owned
By mortals, is the wisest one to use.
[tr. Gibbons/Segal (2000)]

The best thing of all is to practice moderation and worship the gods. That is also, I think, the wisest possession a mortal can make use of.
[tr. Kovacs (2002)]

The greatest wisdom is humility,
It is the greatest gift the gods give us;
Most wise the man who uses it.
[tr. Teevan (2002)]

Wisdom and respect for the gods is a great virtue and a possession most worthy for the mortals to have.
[tr. Theodoridis (2005)]

For having a mind that respects the affairs of divine ones
is the most beautiful thing on earth, and I think
it is the wisest thing someone could do.
[tr. Valerie (2005)]

The best thing is to keep one's mind controlled,
and worship all that comes down from the gods.
That, in my view, is the wisest custom,
for those who can conduct their lives that way.
[tr. Johnston (2008), l. 1428ff]

This is another lesson:
that moderation and reverence for the gods
are a mortal's best possession.
[tr. Robertson (2014), l. 1149ff]

For I believe
that our most beautiful possessions are sanity and a love of the gods.
The wise are those who use wisdom.
[tr. Behr/Foster (2019)]

Balance [sōphroneîn] and reverence for the affairs of the gods is best. I think this is the most sophon possession for mortals’ use.
[tr. Buckley/Sens/Nagy (2020)]

Humility, a sense of reverence before the sons of heaven --
of all the prizes that a mortal man might win
these, I say, are wisest; these are best.
[Bartlett's]