The Gods have proclaimed laws; ethical guidelines at least. They can be followed to a tee and if one does, one might expect the Gods to reward that person. I think we all expect that, deep down. Euripides, after all, in 'Elektra' had Castor proclaim the following at the very end:
"As we go through the plains of the air,
we do not come to the aid of those who are polluted;
but we save and release from severe hardships
those who love piety and justice in their ways of life.
And so, let no one wish to act unjustly,
or set sail with perjurers; as a god,
I give this address to mortals." [1341]

And yet, some of the Gods' most loyal followers seem unable to ever catch a break. They struggle with health, money, friendships, love... and along the way, they begin to doubt. They might doubt themselves at first--question if they are, indeed, practicing right, if they are, indeed, pleasing the Gods--and then the Gods. They might question their fairness, Their judgement... and perhaps Their very existence. It is, after all, the age old question: why do the Gods take care of some but not of others? We are not the first to ponder this. Xenophon, in 'Oeconomicos' wrote:'

"I seem to realise that, while the gods have made it im-
possible for men to prosper without knowing and
attending to the things they ought to do, to some of
the wise and careful they grant prosperity, and to
some deny it." [11.8]

No one has a clear cut answer. Even the ancient Hellenes accepted this faith as was. Xenophon goes on to say:

"...and therefore I begin by worshipping
the gods, and try to conduct myself in such a way
that I may have health and strength in answer to
my prayers, the respect of my fellow-citizens, the
affection of my friends, safety with honour in war,
and wealth increased by honest means." [11.8]

So why do we do it? Why do we foollow proper practice? Why do we sacrifice and labour like Xenophon wrote? Antiphon, in his 'On the Choreutes' says it best, I feel:

"Most of the life of man rests upon hope;
and by defying the gods
and committing transgressions against them,
he would rob himself even of hope,
the greatest of human blessings." [5]