Theory:

     He rode on for a long time till he came to the other side of the forest. Very tired by now, he got off his horse and sat down under a tree that stood near a cave. Suddenly he heard a voice cry out, “Quick! Hurry up! There’s someone under the tree. Come and take his jewels and his horse. Hurry, or else he’ll slip away.” The king was amazed. He looked up and saw a big, brown bird on the tree under which he was sitting. He also heard faint noises issuing from the cave. He quickly got on to his horse and rode away as fast as he could.
Explanation:
 
The king kept riding and reached the other side of the forest. He got down from his horse as he was exhausted and sat under a tree near the cave. All of a sudden, he heard a voice asking to be swift and rob the person outside of his everything, including jewels, horses. The king was shocked to listen to that and looked up to look over. He noticed a big, brown bird on that tree and indistinct noises coming from the cave. Speedily he mounted the horse and ran away.
 
Meanings of difficult words:
  
Numbers
Word
Meanings
1.
AmazedSurprised.
2.
QuicklySpeedily.
Reference:
National Council of Educational Research and Training (2006). A Pact With The Sun. A Tale of Two Birds (pp. 01-03). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.