Is there a single word for the act of a believer temporarily ignoring, or failing to worship, (any) God?
For instance: "God is becoming vengeful due to your [lack of worship]."
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Sign up to join this communityGod is becoming vengeful due to your lack of piety.
This implies lack of actions, not lack of belief; the protagonist is not necessarily an atheist or an apostate.
From wikipedia piety is
noun - spiritual terminology, piety is a virtue that may include religious devotion, spirituality, or a mixture of both.
and
The word piety comes from the Latin word pietas, the noun form of the adjective pius (which means "devout" or "dutiful"). Pietas in traditional Latin usage expressed a complex, highly valued Roman virtue; a man with pietas respected his responsibilities to gods, country, parents, and kin.
"God is becoming vengeful due to your backsliding".
backslide: to lapse morally or in the practice of religion
Here are three words:
"Unfaithfulness" "Repent from your acts of unfaithfulness"
Faith is often used as if it simply meant belief, but it actually "implies unswerving adherence". Unfaithfulness (or the more Latin Infidelity) appropriately describes any relationship (spiritual, marital, etc.) that sees lapses of devotion, attention improperly directed elsewhere, or all forms of disloyalty.
irreverence
would be one possibility.
a. The fact or quality of being irreverent; absence or violation of reverence; disrespect to a person or thing held sacred or worthy of honour.
from the OED.
There is an adjective for people who are a member of a faith but are not actively engaged with it:
non-practising
Brought up as a member of a particular religion but not following its rules and practices
a non-practising Catholic
I didn't see a source on a noun form that retains the religious connection, but you could write your sentence as
God is becoming vengeful due to your nonpractising nature.
lack of faith
enlightenment