I have been told that Muslims must keep their finger nails trimmed. I must tell you that I am a sincere student of Islam. As a woman, I would like to know the reason behind this directive. Also, whether I can grow my finger nails if I can manage to keep them neat and tidy?
It needs to be appreciated that the real message of Islam is purification. Islam wants a person to remain physically as well as spiritually clean. While for spiritual cleanliness it has given us a whole system of worshipping the Almighty, for physical cleanliness it has prescribed certain directives like shaving off hair under the arm pits and around the private parts. Similarly, for the very purpose of hygiene it has directed their male offspring to be circumcised. Keeping nails trimmed is another directive given for the same reason.
As far as the second part of your question is concerned, it needs to be appreciated that it is only the prerogative of the Sharī‘ah to determine the extent of cleanliness required in certain areas, for in such areas human intellect is unable to reach with certainty the required standard of cleanliness. So just as the Sharī‘ah has told us to shave off the hair around the private parts rather than allowing us to maintain clean grown hair around them in order to achieve the required standard of cleanliness, it has told us to trim the finger nails rather than allowing us to maintain clean grown nails in order to achieve this objective.