This is the 2081st most frequent Chinese word.
凭
"凭" means "to rely on," "to depend on," or "by means of."
In this sentence, '凭' is used to indicate relying on or using something as a basis or condition, in this case the ID card, to achieve an action (entering the library).
凭身份证进入图书馆。
Enter the library with an ID card.
Here, '凭' expresses the means or condition by which the subject achieved the action, indicating reliance on personal effort.
我凭自己的努力考上了大学。
I got into university through my own efforts.
In this context, '凭' conveys the meaning of justification or evidence for an assertion.