As you already know, simple past tense of the verb is used to depict an action or event that occurred and was completed in the past. However, when you want to specify an event that happened before another event was completed in the past, the past perfect tense of the verb is used.
The following shows the uses of past perfect tense:
To show that an action happened in the past before another event or action took place. The words when, after, already, just, yet, and as soon as are usually used with the past perfect tense.
Example:
When the Lord God made the earth and the heavens, no shrub had yet appeared on the earth.
In the sentence, there are two past actions: made and had appeared. The simple past tense is combined with past perfect tense to show which of the two actions happened earlier.
To show an action that happened before a definite time in the past
Example:
Six days of work had passed before God rested.
To report a person’s words or thoughts or reported speech
Example:
God said that he had entrusted all his creations to the man.
To point out conditional or hypothetical situations
Example: