What is sunderkand ?
Sunderkand is the fifth chapter of the Hindu holy book called ‘Ramayan’.
The Ramayana has been divided into following chapters by Tulsidas as per the events and importance of the life of lord shri Ram.
What does it contains ?
When Rama sets out for searching Sita towards lanka, they were at the bank of sea at Rameshwar and were planning how to cross the sea.
Jamwant reminded Shree Hanumanji of having a divine power of flying, Shree Hanumanji sets out towards lanka in search of Sitaji.
This is the commencement of sunderkand. On the way Hanumanji met lots of obstacles in the form of she demon Sursa than lankini, however He successfully reaches lanka by over powering them.
On reaching He meets Vibhishan [brother of Ravana] where he tells Hanumanji about the critical situation of Sitaji and told about Ashok Vatika. Hanumanji meets Sitaji after showing the proof of being the ambassador of Shree Rama.
He than destroys the Ashok Vatika [beautiful garden] upon which Ravan gets annoyed and sent his sons to kill Him but in this process one of his son got killed.
However they could overpower Hanumanji who brought Him in front of Ravan. Ravan orders his followers to lit a fire on his tail.
As a result of this the tail went on becoming bigger and bigger and the fire engulfed whole lanka.
After doing this Hanumanji went to meet Sitaji and said He will come with lord Ram to rescue her.
Hanumanji narrated total incident to lord Rama on returning from Lanka.
Upon this Rama started his journey towards lanka by creating Ram setu [BRIDGE] on the sea and enters lanka.
This is the sunderkand being narrated in verses and poetry form.
Why it is supposed to have power ?
As you know this version of Ramayana has been written by shri Tulsidasji.
After completing the end verses of Kishkindhakand he felt that next portion should be written in presence of Shree Hanumanji.
So he started sadhana and upasana and aahwan to which shri Hanumanji accepted and came.
Sunderkand was written in front of shri Hanumanji and at the end of Sunderkand, Tulsidasji requested to imbibe life in this kand by blessing the devotees who recites this kand of freeing from the worldly worries.
This was done by lord Shree Hanumanji. Hence it is powerful.