Thy word is truth, OR, conversely, you could say, Truth (that which is true) is thy word.
It is questionable just how open and truthful humans can be.
As we grow and mature, we are (hopefully) able to tell truth to a deeper level. When we are very immature, we may be only able to tell a surface level (or partial) truth. However, as we grow and mature, that same level of truth would be a lie