The correct option is D indicate that the past cannot be known
The second stanza simply serves to convey that no one person can know another quite as well as they claim to and that one cannot claim to know another's past. In this context, we can say that the imagery here is intended to indicate that the past cannot be known as evidenced by the imagery of "Who shall show us if it was/ Thus indeed in time of old?" So, the answer is option D.