Psalm 45:1 (NKJV)
Today we do most things electronically, but in the past, most things were written out with pen and paper. If you did sit down to write something, would it be normal to expect the pen to start writing on its own? Would you stare at your pen and tell it to get busy writing, or would you start doing the writing yourself, using the pen? You are of course doing the writing, the pen is just the instrument, the method, that you are using to write with; the pen itself is not doing anything, you are doing the writing.
David wrote many of the Psalms and it is easy to see that he was simply expressing what he had in his heart. What David wrote was something that David was thinking about, experiencing, or feeling; David was writing from what was in his heart and mind, not what was in someone else's heart or mind. David could not write about things he did not know, just like a pen cannot write things on its own; David's words came from David, just as our words are coming from us and not someone else.
The things we say are the things we have in our own heart and mind; our tongue is just the instrument we use to express those things. You would not say something and then get upset with your tongue for saying it, you said it based on what you were thinking about, experiencing, or feeling. A pen will not write things on its own, and our tongue is not just going to say things we don't allow it to say. We all need to be determined that we will use our tongue and our words to "write" good and godly things for ourselves and others. What will you write with your tongue today? It is up to you.