How important is your speech? Well I would say very! It's the path to fulfilling your destiny/purpose! For all who have read the bible (at least the book of Genesis) we understand that God(the Father) created the universe with HIS words! Whatever He spoke is what was manifested.
How does this relate to us? Remember we were made in HIS image & likeness, and through the death, burial, and resurrection of Christ we are able to do the works that HE did and greater! (John 14:12)
We also know that life and death are in the power of the tongue, and we eat the fruit (words) thereof (be it life or death)!
So it's no wonder that the bible says in John 14:10 "Do you not believe that I am in the Father, and that the Father is in Me? What I am telling you I DO NOT SAY on My own authority and of MY own accord, but the Father Who lives continually in Me does His works." And then Christ made it known in John 16:13 that When the Spirit of Truth comes he will guide us into all truth and He will NOT SPEAK on His own authority but will tell us what He has heard from the Father.
What are we to understand from this? That if Christ made sure to speak only what the Father said and it led him to the fulfillment of His destiny on earth, and He sent the Holy Spirit to us who believe to tell us what the Father is saying concerning us that we may fulfill our destiny on earth, then we must WATCH THE WORDS coming out of our mouth. I mean our destiny depends on it!
Well Christ let it be known in John 17:4 that He brought glory to the Father by completing the work The Father gave Him to do!