Sri M said...

Ajam nirvikalpam nirakaaramekam
Niraanandam anandam advaita purnam
Param nirgunam nirvishesham nireeham
Para brahma roopam Ganesham bhajema.

We know Ganesha with a form.  Ganesha here is being symbolized as a manifestation of that Para Brahman with no forms, definitions nirvikalpam, nirakararoopam, or impurities, nirmalam.  Anandam, advaitam and purnam are a description of the Supreme Brahman. So, we bow down to Ganesha, the manifestation of the Supreme.