It means the Pen, and that it writes is a great favour of Allah to mankind in all circumstances. Use of a favour is its thanksgiving. Use mut ot be an abuse or misuse or extravagant use or miserly use. Dignity of pen is to be maintained by promoting goodness, truth and right conduct. It is not to hurt the feelings of others nor findig daults in them but to show them gracefully the mishandlings in one's behaviour towards h imself and towards others. Politeness cost nothing, be it oral or in writings.
May God Almighty bless with more and more knowledge that enlightens both outside and inside the hearts.