Two grammatical points render a solemn air for the sentence.
～とは (-towa): This postposition indicates that a definition follows of the noun it modifies.
姿 (sugata): This abstract noun means "one being looked at." Appearance is a handy single word but does not suffice as a translation since it connotes superficiality. "The way one does" may be a better translation.
In toto, I would translate the sentence as:
Buddha consists in the way man lives in truth.
For a translation more faithful to the functional relationships between the elements, it seems to me inevitable that English resorts to colloquial style.
You know what Buddha is? If you see someone and they are living in truth, you see Buddha right there.
who has some difficulty telling Buddha from bubba.
Thank you very much Flaminius. What if The slope went from Upper Left to Lower Right (the opposite), would it still be read from right to left? nevertheless, thank you very much. (I guess that's why the spines on japanese books are on the right side and not the left)