Bhramha Purana, while describing about lord vishnu, it tells us why lord Vishnu rest on Sheshanaga.
Scriptures describe Sheshanaga as ‘Kala’ – ‘Sarpa’ also. Sheshanaga is supposed to be a highly poisonous snake. But Lord Vishnu is resting on him without any fear or worries. It is said that it is a symbol of Tamas meaning darkness. It teaches us not to lose patience even while facing the darkness ‘kala’ itself. If the fear overpowers you, it may shatter your peace. The worshipers who want salvation are being indicated to be peaceful in every circumstances.
Why Lord Vishnu holds the Wheel
The Sudarshana Chakra (wheel) always whirls on the finger of Lord Vishnu indicating the continuous cycle of life and death and karmic events in between life and death is controlled by him. Which is why he is called maintainer of the universe. where as Brahma is called Creator of the universe and Shiva is destroyer of the universe.