ك ل م
The most effective speech is the one which transforms you following which you and your actions change i.e. it make definite physical changes in other person.
Allah has endowed all of His creation with speech so every particle has this capability but only few has the power to make transformation in other self.
As Allah has all the power, He certainly has this power and He can transform all of His creation by His speech, so you read:
كن فيكون Be and it became.
وَكَلَّمَ اللَّهُ مُوسَىٰ تَكْلِيمًا — And Allah spoke to Moses so that Moses was transformed both on the soul and physical level including his actions.
And after it when Allah asked Moses to be thankful i.e. شاكرين, it meant that now Moses has this speech to transform other people, the plural signifies the multiplicity of people.
So Allah endows this capability to His Messengers so that listening to them transform people both internally and externally. This fact is borne out by history many times.
This type of speech has another power. It can kill you. It can put an end to you or your actions. In this regard one who actually listen to this type of speech, his wasteful actions, his bad actions and his sinful acts are cutoff from him.
Now every living being in this earth has this capability to a certain extent. In the end of times even small creatures as tiny as an ant will have this capability and it will transform people both psychologically and physically.
دَابَّةً مِّنَ الْأَرْضِ
This creature will serve as a reminder for all the people who will have forgotten Allah. Allah has all the power to make manifest his verses by any of His creature.
Why a small creature will speak in this manner? The reason is YOU.
As the time progress the speech, the talk will increase. This alone is not sufficiently bad but more important is the content of speech. People will talk more and more, loose talk, hearsay, discontent, abusive, hate speech and backbiting will be rampant. Your speech affects your physical particles and disharmonize them. Every particle remembers this vibration pattern. After your physical body disintegrates these particles are included into various other creatures that eventually will assemble into this powerful creature. As your sharp tongue pierce through other person heart, the creature will have the power to pierce through your physical body and make marks and boils.
How to be safe from it. At physical level you will have to drink from exudate of your boil, a sort of auto vaccination. Internally you will have to stop talking, the only speech permissible being that of peace and harmony
يُؤْمِنُ بِآيَاتِنَا فَهُم مُّسْلِمُونَ
Allaw