Unusual looking characters at a temple in Hong Kong? (source)   

It's from the Tsz Shan Monastery in the New Territories in Hong Kong.  And I reading it up-down, left-right, or simply left to right on both levels?  Many thanks to whoever can help.
一生補處

故“一生補處”，乃階地不退轉，功德不斷增長至成佛道之意。
Therefore 'one life make up' means 'accumulate your good deed and merit in this stage (alive as a human) of existence, and eventually achieve enlightenment'