According to Hindu mythology there exist many gods and goddesses. Equally there also existed many demons and rakshasas. They might have possessed them to safeguard people. It is also a symbol of their power and might. It corresponds to even our daily life like having a large army isn’t sufficient but also enough weapons. The gods portray themselves as supreme and powerful and are the protectors of the world.
Each god has promoted one weapon or other. Lord Sri Ram is well versed with Bow and arrow, Lord Krishna is well versed with Bow and arrow and even Gadha Yudham, Lord Hanuman always poses a Gadha. Lord Muruga has the Vel in his hands. Lord Vishnu has the Sudharshana Chakram. Goddess Kali has the Javelin in her hand. So we can see the battery of weapons that were used by the gods.
The depictions of weapons with which the several Hindu goddesses and gods are adorned are all based on Hindu mythology. The description why they carried these weapons even if they were gods and goddesses is also explained by the people who do research on Indian mythological literature.