It is a custom to worship Goddess Lakshmi, Goddess Saraswati & Lord Ganesha together. Lakshmi is the Goddess of Wealth & prosperity while Ganesha is considered the God of intelligence. These three deities are worshipped together to welcome wealth along with intelligence. Logically, Lakshmi and Ganesha have a common quality of bringing in wealth and prosperity. Also Saraswati and Ganesh have a common trait of being patrons of art and music as well as blessing devotees with skills. Hence the three deities are worshipped together as they denote common qualities