The altar is a metaphor for each of us.
On it are found objects that signify the four elements of which we are all composed:
Water….the water bowl
It also holds a statue of the Buddha.
Buddha, which means the enlightened one, is….our enlightened self.
Therefore, whenever we bow to the altar we are, in effect, bowing to our whole self.
This can be a teaching in itself.
In addition to the above, our altar holds the Remembrance Book in which we write names of people or other sentient beings we wish to hold in our practice. The Remembrance Book can be found on the small table outside the daisan room before each sitting (except in the weekday morning sittings) for you to write in names if you wish. It is carried up and placed on the altar at the beginning of the sitting. The names are not read aloud.
More on the Remembrance Book can be found on its front page.
Also, lying in front of the altar, is the shippei, the teaching symbol given to a Zen teacher on transmission.