過にける Sugi ni keru
四十余りは Yosoji amari wa
大空の Ozora no
兎烏の Usagi karasu no
道にこそありける Michi ni koso arikeru
Not vainly spending a moment in twelve hours
Forty some years
have already passed away!
[I have been walking]
the path of the rabbit and the crow
in the boundless firmament.
Dōgen became forty years old in 1240. This waka might have been written a few years later, around the time he moved from Koshoji in Kyoto to Echizen to found a new monastery.
In ancient times in Japan, one day and night was divided into 12 hours and named after twelve animals in the same way as the twelve zodiacal signs. The great poet Daichi Sokei (1290-1366), the sixth generation descendant of Dōgen, wrote this instruction for lay practitioners throughout the twelve hours.
In the Juniji Hogo (Dharma Words for Twelve Hours), Daichi wrote:
"From the Hour of Tiger (3 to 5 am) to the end of the Hour of the Cow (1 to 3 am), throughout one day and night, there is no time to deviate from the continuous practice of the buddha-ancestors. If you spend day and night practicing in accordance with the continuous practice of the buddha-ancestors, twenty or thirty years, or your entire lifetime will be nothing but this one day and night."
"The rabbit" refers to the moon and "the crow" refers to the sun. It is said that in the moon a rabbit is living, and in the sun, there is a crow with three legs. Modern people interpret the crow in the sun as the sunspot. The path of the rabbit and the crow symbolize the repetition of day and night. It also refers to boundless space.
Dōgen Zenji is saying that he has been walking the path of the moon and sun, of time and space. This path is the network of interdependent origination, in which one is interconnected with everything, and following the Buddha's teachings. Being mindful here and now in each moment is how we can avoid spending our time and space in vain.
Dōgen said in Shobogenzo Zuimonki:
"An ancient said, 'Do not spend day and night in vain.' Now I ask you, 'Does the time stop passing if we hold it dear? Or does it continue passing even if we lament? ' I also ask you, 'Does time pass vainly? Or do people spend time in vain?' This means that we should practice the Way without spending time wastefully."