Theory:

     Just then, the other man at the tollgate on the other side ran out, flashing a torch like a madman.

     “Hoy, Hoy, Hoy, Stop!” he cried.

     “What’s the matter?” shouted my master.
  
     “The bridge is broken in the middle. Part of it has been carried away by the flood. If you come any further, you’ll be in the river!”

     “Thank God!” said my master.

     "You really are a Beauty!” said John, as he took hold of my bridle and gently turned me round.

     The wind seemed to have settled down. It grew darker and darker stiller and stiller. I trotted softly along, the wheels hardly making a sound on the soft, wet road.

     Then Master told John that God had given people brains by which they can find things for themselves. He said, however, God had given animals a special knowledge which did not depend on thinking things out and was much quicker to respond to danger. This instinct in animals, he said, had often saved the lives of men.
Explanation:
 
At the same time, a man from the other side of the toll gate ran out, flashing his torchlight like a crazy man. He shouted "Hoy, Hoy, Hoy, Stop!" at them. The horse's master asked him what the matter was. The toll gate man explained that the bridge was broken in the middle. There had been a flood, and a part of the bridge had been washed away. He warned them that if they moved any further, they would fall in the river.
 
broken bridge1_Moment.jpg
"The bridge is broken in the middle. Part of it has been carried away by the flood!"
  
The master thanked God in relief! If the horse had not realized the danger through its instinct, they could have drowned that day!  John appreciated the horse and told him he was a real beauty, as he caught the bridle and softly turned the horse around.
 
By this time, even the wind had calmed down. It grew darker, and it became noiseless and motionless. The horse ran with short steps, softly. The wheels did not make any sound of touching on the ground because the road was soft and wet.
 
Master told John that God had given brains for people so that they can get to know things for themselves. But God had given a special knowledge to animals, who cannot think, but to react quicker in response to any danger. This is called instinct. The in-built power of animals to respond to certain situations is the power of instinct that God had blessed animals with. This instinct has saved the lives of many people in history, said Master to John.
 
Meanings of difficult words:
  
No.
Words
Meanings
1
trottedran with short steps, moved faster than a walking pace
2
stillernot moving or making any sound
3
instinctan innate, typically fixed pattern of behaviour in animals in response to certain stimuli
Reference:
State Council of Educational Research and Training (2019). Term-1 English Standard-8. When Instinct Works - Anna Sewell(pp. 145-151). Published by the Tamil Nadu Textbook and Educational Services Corporation.