Leonard Cohen is famous for his line in “Anthem:”
There is a crack, a crack in everything That's how the light gets in.
He called that line the closest thing he had to a credo.
Keeping that quote in mind as a reference point helps us to understand "Credo." In it, Cohen lives and finds happiness in the crack or crevice in the world between good and evil, between the world's greatest troubles ("a ruined house of bondage") and its dream of perfection: a "holy promised land."
Cohen uses the image of a cloud of grasshoppers, normally seen as a plague that brings destruction, in a positive light--that of the Biblical understanding of the locust plague brought upon the Egyptians by God as what initiated liberation and change. The speaker understands that what looks bad from one perspective can look good from another. Seeing the cloud of grasshoppers leads the speaker to dream of grand things that change the world:
of Pharaoh hanging by the feet
before turning back to the simpler reality of life with his beloved.
Later, when he and his lover are no longer making love, the grasshoppers pass, fat and well-fed. Then, even later, as "battalions of the wretched," inspired with "holy promises" pass the place where the speaker and his lover rest, the speaker thinks he could leave his lover and join the wretched, or perhaps take his lover to the city they have left.
Instead, the speaker decides its best to live in the ordinary world of this moment and stay where he is. He writes
I must not betray
the small oasis where we lie,
though only for a time.
It is good to live between
a ruined house of bondage
and a holy promised land.
Those lines are a celebration of the ordinary moments in life. He says it is good to have experiences that are neither terrible ("a ruined house of bondage") or exalted dreams that have not come to pass "a holy promised land." The now, the real, the here, the beloved: all of this is what is important, while empires come and go--he is glad to hear the "larvae" of the grasshoppers of liberation growing beneath him, but glad to be where he is.