The subject is underlined:
God gives each believer a task.
The word 'believer' is not a verb. It's a noun. We know this because we can replace it with another noun:
God gives each person a task.
Structure
God (subject) gives (verb) each (quantifier) believer (noun) a (determiner) task (noun)
Subject: God
Verb: gives
Indirect Object of the Verb: each believer
Direct Object of the Verb: a task
The direct object and the indirect object can be switched around, like this,
God gives a task to each believer.
God gives each believer a task.