The importance of Himalayas and the Indian Ocean with respect to the climate of India can be explained as follows :
The Indian Ocean and Himalayan ranges play an important role in formation of southeast monsoon winds.
In summers, the temperature in Punjab Plains and the Thar desert is found to be high. As its effect, the areas of low pressure are developed.
On the other hand, the areas of high pressure are found in the Indian Ocean. This leads to formation and flowing of southeast monsoon winds from the Indian Ocean to the mainland of India.
These winds are moisture-laden and so they bring rainfall in India.
Himalayas saves India by obstructing the passage of very cold winds from the north into India in winter.
The southwest monsoon winds flow from the south to the north and reaches towards the Himalayas.
These winds are obstructed by the Himalayas. Due to obstruction, these winds change their direction and start flowing from the northeast to the Indian Ocean.
The return journey of these winds bring the retreating monsoon in peninsular region of India