The perfect tense relates to the past continuing into the present. To fully unpack the interpretation, the ISV should say, "If we say we have never sinned and continue to not sin...."
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Perfect tense means the action is finished. It is the result of that action that continues.
The clock is/has_been broken - the clock was subjected to action that broke it, that action does not continue - the condition that resulted from the action (the state of "broken") does continue.
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Grammar Handbook: Perfect and Progressive Verb Forms
Perfect Form
The perfect form is the verb tense used to indicate a completed, or "perfected," action or condition. Verbs can appear in any one of three perfect tenses: present perfect, past perfect, and future perfect.
Verbs in the perfect form use a form of "have" or "had" + the past participle. (It is the form of the helping verb that indicates the tense.)
Present Perfect: I have finished my homework already.
Grammar Handbook: Perfect and Progressive Verb Forms
Perfect Form
The perfect form is the verb tense used to indicate a completed, or "perfected," action or condition. Verbs can appear in any one of three perfect tenses: present perfect, past perfect, and future perfect.
Verbs in the perfect form use a form of "have" or "had" + the past participle. (It is the form of the helping verb that indicates the tense.)
Present Perfect: I have finished my homework already.
"Doing homework" does not continue.
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